UC-NRLF 


SB    32    331 


A  POPULAR  TREATISE 

ON 

THE  COLLOIDS  IN  THS 
INDUSTRIAL  ARTS 


A&NDT--K 


A  POPULAR  TREATISE  ON 
THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS 


Published  by 

The  Chemical  Publishing  Company 

EASTON,  PA. 

Publishers  of  Scientific  Books 

Engineering  Chemistry  Portland  Cement 

Agricultural  Chemistry  Qualitative  Analysis 

Household    Chemistry  Chemists'  Pocket  Manual 

Metallurgy,  Etc. 


A  Popular  Treatise  on 
The  Colloids  in  the  Industrial  Arts 


BY 


PROF.  DR.  KURT  ARNDT 

Privat-Dozent  at  the  Technuche  Hochschule,  Berlin,  Germany 
Translated  from  the  Second  Enlarged  German  Edition  by 

NAHUM  E.  KATZ,  B.Sc. 

Chemist  to  Eagle  Cotton  Oil  Company.  Meridian,  Miss. 
Member  of  the  American  Chemical  Society 


EASTON,  PA.: 

THE  CHEMICAL  PUBLISHING  CO. 
1914 

LONDON,    ENGLAND : 

WILLIAMS  A,  NORGATE 

14    HENRIETTA  STREET,    COVENT  GARDEN,  W.  C. 


TT1 

A 


COPYRIGHT,  1914,  BY  EDWARD  HART. 


TABLE  OF  CONTENTS. 


Translator's  Preface iv 

Preface v 

Preface  to  the  Second  German  Edition vi 

Definition  of  the  Term  "Colloid" i 

Colloidal  Solutions 2 

Colloidal  Solutions  of  Metals 4 

Flocculation  of  Colloidal  Solutions  8 

Reversible  and  Irreversible  States  of  Aggregation 12 

General  Remarks  on  Dispersed  Systems 14 

Suspension-  and  Emulsion-Colloids 16 

Ruby-Glass   18 

Milky- White  Opaque  Glass.     Troostite.     Phosphorus 21 

Colloids  in  the  Mineral  Kingdom 23 

Silver-  and  Gold-Mirrors 25 

Manufacture  of  Tungsten  Lamps 26 

Colloids  in  the  Ceramic  Industry  32 

Colloids  in  the  Hydraulic-Cement  Industry 35 

Colloids  as  Adhesives  and  Glues 38 

Usefulness  of  the  Colloids  in  the  Absorption  of  Liquids 39 

Dehydration  of  Peat  by  Electro-Osmosis 40 

Colloids  as  Diaphragms  and  Filters 41 

Adsorption 42 

Varnish-Making 44 

Dyeing   44 

Tanning 47 

Soap  Manufacture 50 

Brewing  Industry 52 

Lubricating  Greases 53 

Sewage  Purification 55 

Colloids  in  Agriculture 57 

Index 61 


300345 


TRANSLATOR'S  PREFACE. 


The  warm  reception  and  great  approval  with  which 
the  little  volume  of  Prof.  Dr.  Kurt  Arndt's  "Die 
Bedeutung  der  Kolloide  fur  die  Technik"  met  in  Ger- 
many make  it  very  desirable  that  it  becomes  accessible 
also  to  the  English-speaking  chemists.  It  will  be  es- 
pecially welcomed  by  those  busy  works-chemists  who  do 
not  have  the  time  to  make  a  special  study  of  the  chem- 
istry of  the  colloids,  but  who  desire  to  keep  abreast  with 
the  development  of  their  science  and  the  application  of 
its  various  theories  in  the  different  industries. 

This  translation  has  been  made  from  the  second  Ger- 
man edition  which  has  been  revised  and  considerably  en- 
larged by  the  author.  It  was  thought  advisable  to  add 
an  Index,  which  is  missing  in  the  German  edition. 

I  feel  it  a  pleasant  duty  to  express  here  my  thanks 
to  the  publisher  of  this  translation,  Prof.  Dr.  Edward 
Hart,  proprietor  of  the  Chemical  Publishing  Company, 
for  his  revision  of  my  manuscript  and  for  the  great  care 
in  the  preparation  of  the  book  for  publication. 

NAHUM  E.  KATZ. 

MERIDAN,  Miss.,  January,  1913. 


PREFACE. 

The  present  treatise  originated  from  a  lecture,  which 
I  delivered  before  the  "Verein  zur  Befoerderung  des 
Gewerbefleisses,"  in  Berlin.  Since  this  short  lecture  was 
favored  with  a  very  detailed  abstract  in  the  "Chemiker- 
Zeitung,"  and,  since  it  found  otherwise  more  attention 
than  expected,  I  willingly  complied  with  the  request  of 
the  energetic  publisher  of  the  "Kolloid-Zeitschrift"  to 
make  my  lecture  accessible  to  larger  circles,  and  to  pre- 
sent a  popular  treatment  of  the  subject  of  the  intimate 
relation  between  colloidal  chemistry  and  the  Arts  and 
Manufactures,  in  a  separately  issued  volume.  The 
chemist,  who  makes  a  special  study  of  colloidal  chem- 
istry, will  naturally  find  in  the  present  unassuming 
treatise  little  which  is  new  to  him. 

Since  the  purely  scientific  problems  of  colloidal  chem- 
istry were  treated  in  the  "Introduction  To  Colloidal 
Chemistry"  by  Poschl,1  I  was  in  the  position  to  limit 
myself  to  short  introductory  remarks  in  explanation  of 
the  most  important  ideas  and  terms,  after  which  I  entered 
into  a  more  thorough  discussion  of  technical  matters.  I 
have  brought  together  a  large  quantity  of  material,  which 
I  have  taken  from  technical  magazines  (preferably, 
from  the  "Zeitschrift  fur  Chemie  und  Industrie  der  Kol- 
loide"),  partly  from  the  book  by  A.  Miiller,  "Allgemeine 
Chemie  der  Kolloide,"  (Leipzig,  1907),  partly  from  my 
own  book,  "Technische  Anwendungen  der  physikalischen 
1  This  book  has  been  translated  into  English. 


VI  PREFACE 

Chemie,"  (Berlin,  1907),  but  I  have  not  striven  after 
completeness,  but  endeavored,  to  give  the  reader  a  Vivid 
Picture  of  the  Great  Significance,  which  the  colloids  have 
in  numerous  important  processes.  K.  ARNDT. 

Charlottenburg,  New- Year,  1909. 


PREFACE  TO  THE  SECOND  GERMAN  EDITION. 


In  the  two  years,  since  the  first  edition  of  this  treatise 
appeared,  colloidal  chemistry  has  rapidly  developed. 
Numerous  treatises,  preferably,  in  the  "Zeitschrift  fur  die 
Chemie  und  Industrie  der  Kolloide"  and  their  "Chem- 
ische  Beihefte,"  have  brought  forth  much  which  is 
of  interest,  and  some  which  is  of  value  to  the  indus- 
tries. I  have  endeavored  to  do  justice  to  all  these  devel- 
opments within  the  scope  of  my  treatise,  by  changes  and 
considerable  additions.  The  chapters  on  Dispersed 
Systems,  Suspension-  and  Emulsion-colloids,  in  which  I 
duly  considered  the  new  classification  of  colloidal  chem- 
istry and  its  terms,  and,  the  chapter  on  the  Colloids  in 
the  Mineral-kingdom,  and  in  the  Brewing-Industry  are 
new. 

To  those  who  desire  further  information  about  scien- 
tific colloidal  chemistry,  the  "Grundriss  der  Kolloid- 
chemie"  by  W.  Ostwald,  (Dresden,  1911),  the  second 
edition  of  which  has  just  appeared,  may  be  recom- 
mended.1 

K.  ARNDT. 

Charlottenburg,  Easter,   1911. 
1  A  third  edition  of  this  book  has  already  appeared. 


1.  Definition  of  the  Term  "Colloid."— The  name 
"Colloid"  is  connected  with  the  Greek  word  KoAAa  = 
glue,  and  means  "glue-like";  it  was  first  used  by  Th. 
Graham  half  a  century  ago.  This  English  chemist 
termed  as  Colloids  various  substances,  which,  indeed, 
chemically,  have  nothing  to  do  with  glue,  but  which  re- 
semble in  appearance  the  soaked-up  cabinet-maker's  glue^ 
as,  for  instance,  the  gelatinous  precipitate  which  is  ob- 
tained when  muriatic  acid  is  added  to  a  concentrated 
solution  of  waterglass.  From  sodium  silicate,  hydro- 
chloric acid  separates  a  voluminous  jelly,  which,  by  wash- 
ing, we  can  free  almost  completely  from  the  salt.  By 
heating,  we  gradually  expel  the  large  quantity  of  water 
which  is  absorbed  by  the  jelly,  and  at  last  obtain  a  pul- 
verulent mass  which  gives  off  the  last  traces  of  its  water 
only  when  it  is  strongly  ignited.  Heated  over  an  oxy- 
hydrogen  flame  the  silicic  acid  melts  and  on  cooling  con- 
geals to  a  transparent  glass,  quartz  glass.  But  if  we  let  the 
mass  cool  extremely  slowly,  then  the  quartz-glass  trans- 
forms into  small  crystals.  So  we  have  for  one  and  same 
substance,  silicic  acid,  three  different  states:  the  col- 
loidal,  the  glassy  and  the  crystalline  state.  In  a 
strict  sense,  silicic  acid  has  several  crystalline  states, 
since  it  is  found  in  several  crystalline  forms,  of  which 
rock-crystal  presents  an  especially  beautiful  example. 
One  of  these  states,  the  hexagonal  crystalline  form  of 


2  THE  COI^OIDS  IN  THE  INDUSTRIAL  ARTS 

rock-crystal,  is,  at  the  ordinary  temperature,  the  state 
of  rest  of  silicic  acid  into  which  the  other  forms  tend  to 
change. 

The  glassy  state  forms  a  continuation  of  the  liquid 
state;  the  glasses  are  considered  as  liquids  which  have  a 
very  great  internal  friction.  The  colloidal  state,  on 
the  contrary,  may  be  defined  as  the  solid  non-crystal- 
line state;  we  really  cannot  call  it  amorphous,  form- 
less, because,  as  was  shown  by  C.  Biitschli,  colloidal 
silicic  acid  presents  a  very  fine  cell-structure.  It 
has  a  honey-comb  (wabige)  structure,  and  therefore,  like 
a  sponge,  it  is  able  to  absorb  liquids.  Such  a  cell-struc- 
ture of  great  surface  development  is  shown  by  numerous 
inorganic  and  organic  jellies,  particularly  the  cells  of  veg- 
etable and  animal  bodies,  and  of  substances  which  are 
obtained  from  them:  wool,  and  other  textile  fibers, 
leather,  glue,  caoutchouc,  cellulose  and  celluloid,  pro- 
teins; all  come  under  the  term  colloid.  How  infinite 
the  field.1  The  reader  will  anticipate  that  the  industrial 
arts  as  well,  have  much  to  do  with  "Colloids,"  although 
up  to  the  present  time  they  have  generally  not  made  use 
of  this  name. 

2.  Colloidal  Solutions. — If  we  add  muriatic  acid  to  a 
dilute  solution  of  waterglass,  no  jelly  separates,  but  after 

1  It  is  accepted  at  present  that  all  substances  are  able,  under 
appropriate  conditions,  to  assume  the  colloidal  state. 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  3 

evaporating  the  solution,  it  congeals  suddenly  with  sep- 
aration of  silicic  acid.  In  spite  of  the  fact  that  from 
the  dilute  solution  no  silicic  acid  visibly  separates,  the 
sodium  silicate  and  the  hydrochloric  acid  have  neverthe- 
less entered  into  a  chemical  inter-action;  this  can  be 
proven  by  physical  measurements.  For  instance,  by 
measuring  the  electrical  conductivity  of  the  solution. 
We  have  in  this  case  a  colloidal  solution.  We  can  re- 
move the  salt  from  this  solution  by  transferring  the  latter 
into  a  vessel,  the  bottom  of  which  is  formed  of  a  parch- 
ment membrane,  and  placing  it  in  pure  water.  The  salt 
diffuses  through  the  membrane,  while  the  colloidal  silicic 
acid  does  not.  In  this  way,  by  Dialysis,  we  are  able,  if 
we  renew  the  water  from  time  to  time,  to  obtain  a  col- 
loidal solution  of  silicic  acid  which  contains  only  traces  of 
salt.  By  evaporation  we  can  concentrate  it  to  a  certain 
degree.  But  the  more  concentrated  the  solution  becomes 
the  easier  it  congeals.  We  can  coagulate  it,  for  instance, 
immediately,  by  adding  to  it  a  minute  quantity  of  soda, 
or  by  passing  into  it  only  a  few  bubbles  of  carbonic  acid 
gas.  This  colloidal  solution  of  silicic  acid  manifests 
besides  its  remarkable  instability,  still  other  very  impor- 
tant differences  from  a  true  solution,  for  instance,  that 
of  common  salt.  While  a  solution  of  salt  boils  only 
above  100°  C.  and  freezes  below  o°  C.,  the  boiling  and 
freezing  points,  the  vapor  tension  and  electrical  conduc- 


4  TH£  COIvLOIDS  IN  THE)  INDUSTRIAL  ARTS 

tivity  of  the  colloidal  solution  are  not  much  different 
from  those  of  pure  water. 

For  colloidal  solutions  Graham  introduced  the  name 
Sol;1  when  water  is  the  solvent,  the  name  became 
Hydrosol.  Correspondingly  there  are  Alcosols,  etc. 
The  precipitated  colloid  on  the  contrary  was  a  Gel.2 

Like  the  hydrosols  of  silicic  acid,  the  hydrosols  of  iron 
hydroxide,  aluminium  hydroxide,  stannic  acid,  tungstic 
acid,  arsenious  sulphide,  Berlin  blue,  etc.,  can  be  obtained 
by  chemical  transformation  in  dilute  solutions  and  puri- 
fied by  dialysis. 

3.  Colloidal  Solutions  of  Metals. — Metals  may  also  be 
obtained  in  the  condition  of  colloidal  solutions,  when 
their  salts  in  very  dilute  solution  are  reduced  to  metals. 
In  this  way,  the  great  physicist  M.  Faraday,  as  early  as 
1857,  obtained  a  colloidal  solution  of  gold  when  he 
treated  a  very  dilute  solution  of  gold-chloride  with  yel- 
low phosphorus.  A  very  good  method  for  the  prepara- 
tion of  colloidal  solutions  of  gold  is  given  by  R.  Zsigmon- 
dy,  who  studied  these  solutions  very  thoroughly,  and  even 
devoted  to  them  a  special  book.3  He  employs  formalde- 
hyde as  the  reducing  agent  and  by  a  small  addition  of 
potash  increases  the  stability  of  the  colloidal  solution. 

1  From  "Solution." 

2  From  "Gelatine." 

8  R.  Zsigmondy,  Zur  Erkenntins  der  Kolloide  (Jena  1905). 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  5 

If  the  water  employed  in  this  process  is  sufficiently  free 
from  impurities,  a  colloidal  solution  of  gold  is  obtained 
which  has  a  magnificent  deep-red  color  and  which  will 
keep  for  years.  In  reflected  light,  on  the  contrary,  this 
solution  has  a  dirty  brown  color.  This  turbidity  is  an 
indication  that  in  this  case  we  do  not  have  a  true  solu- 
tion, but  that  in  the  water  solid  particles  which  reflect 
the  light  are  suspended.  If  the  colloidal  solution  is  illu- 
minated by  a  very  bright  light,  then  the  separate  gold- 
particles  can  even  be  seen  under  a  microscope.  v 

H.  Siedentopf,  of  Jena,  constructed  for  this  purpose 
the  following  appliance:  strong  arc-light,  or  still  better, 
sun-light  is  condensed  by  lenses  to  a  light-cone  with  a 
perpendicular  axis,  the  point  of  which  falls  into  the  solu- 
tion to  be  tested.  The  microscope  is  focused  on  the  point 
of  the  light-cone,  the  place  where  the  greatest  brightness 
prevails.  In  pure,  dust-free  water  the  vision  field  re- 
mains dark ;  in  the  colloidal  solution  of  gold,  on  the  con- 
trary, numerous  brilliantly  variegated  red,  yellow,  and 
green  discs  are  seen,  which  restlessly  fly  to  and  fro  in  a 
constant  zig-zag  movement.1 

If  the  visible  gold-particles  in  a  limited  space  are 
counted  and  the  quantity  of  gold  in  this  space  is  deter- 
1  The  brightness  of  the  ultra-microscopic  vision  was  consider- 
ably enhanced  by  the  introduction  of  the  Paraboloid-  and  Kardioid- 
Condensers.  Now  even  very  small  quantities  of  solution  are 
sufficient. 


6  THE  COLLOIDS  IN  THE:  INDUSTRIAL  ARTS 

mined  by  analysis,  then  the  average  size  of  these  par- 
ticles can  be  calculated.  If  it  be  assumed  that  these  par- 
ticles are  spherical,  it  is  found  that  their  diameters  in 
different  solutions  of  gold  range  from  about  10  to  40  /A/*.1 
This  size  is  far  under  the  limit  of  visibility  under  an 
ordinary  microscope.  For  this  reason  H.  Siedentopf 
named  his  appliance  Ultra-microscope  and  termed  the 
particles  which  are  made  visible  by  it,  ultra-  or  submi-> 
croscopic  From  the  fact  that  the  gold-particles  appear 
as  small  discs  nothing  can  be  concluded  as  to  their  real 
form ;  this  is  due  only  to  the  imperfections  of  our  vision.2 

In  light  red  solutions  of  gold,  R.  Zsigmondy  was  able 
to  point  out  still  smaller  particles,  down  to  6  /A/U,.  In 
others  he  found  also  larger  particles,  up  to  200  /*/&;  these 
solutions  already  began  to  disintegrate,  the  gold  particles 
clumped  together  to  larger  complexes  and  were  gradually 
sinking  to  the  bottom. 

In  two  interesting  graphical  descriptions,  in  his  above- 
mentioned  book,  R.  Zsigmondy  compared  the  magnitude 
of  these  ultra-microscopical  gold  particles,  on  the  one 
hand,  with  microscopically  small  objects,  such  as  blood 
corpuscles,  starch  particles,  suspensions  of  porcelain 
clay,  bacteria,  on  the  other  hand,  with  the  still  smaller 
(calculated)  dimensions  of  the  molecules  of  chloroform, 

1  /A  is  the  sign  for  one  millionth  part  of  one  millimeter  (micron). 

2  The  stars  also  appear  to  us,  not  as  points,  but  as  small  discs. 


THE:  COLLOIDS  IN  THE:  INDUSTRIAL  ARTS  7 

alcohol,  etc.  We  learn  from  this  comparison  that,  in 
general,  the  molecules  are  still  very  much  smaller  than 
the  ultra-microscopical  gold-particles,  but  that  very 
large  molecules,  which  comprise  very  many  atoms,  such 
as,  for  example,  the  molecule  of  soluble  starch  (accord- 
ing to  C  A.  Lobry  de  Bruyn)  are  much  like  them.  The 
ultra-microscope  has  considerably  shifted  the  limits  be- 
tween visible  and  invisible.  In  several  pink-colored  solu- 
tions of  gold  the  existence  of  mass-particles  even  still 
smaller  than  6  ftp.  must  be  assumed.  Indeed,  these  par- 
ticles can  no  more  be  seen  separately  by  means  of  the 
ultra-microscope,  but  their  presence  is  detected  by  a 
feeble  glittering  of  the  light;  R.  Zsigmondy  terms  these 
particles  amicroscopic.1  If  a  few  drops  of  the  usual 
colloidal  solution  of  gold  are  added  to  such  an  amicro- 
scopic  solution  of  metallic  gold,  the  flocculation  of  the 
latter  is  considerably  accelerated. 

Another  way  of  preparing  the  hydrosols  of  metals, 
worked  out  by  G.  Bredig,  is  the  following:  an  electric 
arc  or  strong  sparks  are  formed  under  water  between 
two  wires  of  the  respective  metal;  the  metal  then  evap- 
orates and  partially  remains  in  the  water  as  a  colloidal 

1  The  lower  limit  of  visibility  of  metallic  particles  is  especially 
favorably  located  because  these  particles  reflect  the  light  rays  very 
strongly.  The  molecule  of  soluble  starch,  despite  its  large  size, 
will  be  invisible  under  the  ultra-microscope,  because  it  does  not 
shine  sufficiently  bright. 

2 


8  THE  COIAOIDS  IN  THE  INDUSTRIAL  ARTS 

solution;  another  part  clumps  together  and  sinks  to  the 
bottom.  The  solution  of  gold,  obtained  in  this  way,  is 
usually  colored  violet  blue.  Most  of  the  metals  have 
been  prepared  in  this  second  way  in  the  condition  of 
colloidal  solutions  in  water  and  in  other  liquids.  So, 
for  instance,  Th.  Svedberg  prepared  a  blue  colloidal  solu- 
tion of  metallic  sodium  in  ligroin.  But  none  of  these 
numerous  solutions  can  be  compared  in  beauty  of  color- 
ation with  that  of  the  solution  of  gold.  A  colloidal  solu- 
tion of  platinum,  for  example,  appears  yellowish  brown 
in  transmitted  light  and  almost  black  in  reflected  light. 
The  hydrosol  of  silver  has  a  brick-red  color.  Most  of 
the  colloidal  solutions  of  metals  are  very  instable  and 
soon  precipitate  the  metal. 

4.  Flocculation  of  Colloidal  Solutions. — Since  the  col- 
loidal solutions  do  not  correspond  to  any  condition  of 
equilibrium  and  their  particles  tend  to  clump  together, 
the  colloid  flocculates  by  itself  in  a  longer  or  shorter 
period ;  boiling  usually  accelerates  this  decomposition. 

A  small  addition  of  an  alkali  to  the  water  considerably 
increases  the  keeping  qualities  of  the  metallic  Sols.  The 
Sol  of  silicic  acid,  on  the  contrary,  becomes  more  stable 
by  the  addition  of  some  hydrochloric  acid.  Some  in- 
vestigators assert  that,  in  general,  the  presence  of  cer- 
tain small  quantities  of  "electrolytes"  is  needed  for  the 
existence  of  colloidal  solutions.  At  any  rate,  it  is  a  fact, 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  9 

that  most  of  these  solutions  are  very  sensitive  towards 
any  change  in  the  quantity  of  electrolytes,  which  they 
contain ;  for  example,  the  red  solution  of  gold  is  colored 
blue  by  the  addition  of  one  drop  of  hydrochloric  acid, 
and  the  gold  gradually  separates. 

The  quantity  of  the  addition,  which  causes  the  change 
in  the  coloration,  or  the  beginning  of  precipitation,  varies 
with  the  nature  of  the  solution  and  that  of  the  addition. 
Quantities  of  electrolytes,  which  remain  below  this  limit, 
the  swelling  value  (Schwellenwert),  will  not  cause 
the  flocculation  of  the  hydrosol  even  in  a  longer  period. 
The  explanation  of  this  phenomena  at  present  preferred, 
is  based  on  the  fact,  that  colloids,  as,  in  general,  all  solid 
particles,  move  in  the  field  of  an  electrical  current.  If 
we  send  a  current,  having  a  pressure  of  about  no  Volts, 
or  more,  through  a  colloidal  solution,  it  is  observed,  that 
the  solution  is  almost  a  non  conductor,  but  that  the  col- 
loidal particles  collect  at  one  pole.1  Colloidal  metals 

1  While  the  mass  particles  of  the  colloid  migrate  together 
towards  one  and  the  same  pole,  in  solutions  of  "electrolytes,"  one 
part  of  the  molecules  migrates  toward  one,  and  the  other  part — 
towards  the  other  pole ;  for  example,  the  chlorine  of  hydrochloric 
acid  migrates  towards  the  positive  pole  (Anode),  and  the  hydrogen, 
towards  the  negative  pole  (Kathode).  In  accordance  with  this, 
the  ionic  theory  assumes  that  the  hydrochloric  acid  is  split  into 
negatively  charged  chlorine-ions  and  positively  charged  hydrogen- 
ions.  Potassium  hydroxide  (caustic  potash),  when  dissolved  in 
water,  is  split  into  positive  potassium-ions  and  negative  hydroxyl- 
ions. 


IO  THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS 

usually  migrate  towards  the  positive  pole,  the  Anode; 
therefore  they  are  negatively  charged ;  since  (as  is  known 
from  friction  electricity)  opposite  electricities  attract 
each  other.  Iron  hydroxide  and  aluminium  hydroxide, 
on  the  contrary,  migrate  towards  the  cathode,  and  are 
therefore  positively  charged.  More  accurate  observa- 
tions revealed  the  fact,  that, "migration-sense"  (Wander- 
ungssinn)  is  not  so  much  dependent  on  the  kind  of  the 
colloid,  but  that  it  is  determined  mostly  by  the  small 
quantities  of  electrolytes,  which  are  found  even  in  very 
pure  solutions.  A  very  small  increase  of  the  hydrogen- 
ions  in  the  water  electrifies  the  hydrosol  positively  so 
that  its  particles  migrate  towards  the  negative  pole;  a 
minute  increase  of  the  hydroxyl-ions  electrifies  it,  on  the 
contrary,  negatively  so  that  its  particles  migrate  towards 
the  positive  pole. 

An  addition  of  ions,  which  carry  a  charge  opposite  to 
that  of  the  colloidal  particles,  causes  their  precipitation;1 
so  a  negatively  charged  colloid  is  coagulated  by  positively 
charged  ions.     Similarly  charged  ions  cause  no  precipi-  , 
tation,  or  have  a  slight  protective  action.  ^^^^^ 

Hydrosols   which   carry   opposite   charges   precipitate 
each  other;  so,  for  example,  colloidal  solutions  of  gold 

1  The  precipitating  power  of  the  respective  ion  is  the  greater 
the  higher  its  chemical  valence ;  a  bivalent  ion  acts  more  than 
one-and-a-half  times  as  strongly  as  a  univalent  one.  But  hydro- 
gen- and  hydroxyl-ions  possess  the  greatest  precipitating  power. 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  II 

and  of  stannic  acid  give  a  purple  precipitate  which  corres- 
ponds to  the  well  known  purple  of  Cassius.  If  a  larger 
quantity  of  the  oppositely  charged  colloid  is  added  to  the 
solution,  often  no  precipitation  occurs,  on  the  contrary 
the  solution  becomes  more  stable.  Especially  organic 
colloids,  such  as  gelatine  and  proteins,  increase  the  sta- 
bility of  colloidal  metals;  therefore  these  are  termed 
protective  colloids.  The  pharmaceutical  industry  is 
making  use  of  these  colloids  in  the  manufacture  of  col- 
loidal silver  and  mercury.1  We  have  seen  in  the  example 
of  hydrosol  of  gold,  which  becomes  more  stable  by  the 
addition  of  a  little  alkali  (i.  e.,  hydroxyl-ions)  that  sim- 
ilarly charged  ions  also  make  a  colloidal  solution  more 
stable,  if  they  are  added  in  a  sufficiently  small  quantity. 

The  flocculation  processes  are  of  paramount  impor- 
tance in  physiological  chemistry;  here  belongs,  for  in- 
stance, the  mutual  precipitation  of  toxins  and  antitoxins 
( Immuno-serum  ) . 

Singular  is  the  behavior  of  solutions  of  proteins.  If 
the  protein  solution  is  purified  from  salts,  as  much  as 

1  This  protective  action  is  manifested  also  in  very  fine  mechan- 
ical suspensions,  as,  for  example,  in  a  suspension  of  soot  in  water. 
Despite  its  very  fine  division,  soot  can  be  prevented  from  precipi- 
tating only  by  a  protective  colloid  (lime),  which  fact  is  taken  into 
consideration'  in  the  manufacture  of  water  colors.  In  a  similar 
manner  Acheson  was  able,  by  treating  his  graphite  with  tannic 
acid  and  water,  to  bring  it  into  such  a  condition  that  it  could  be 
permanently  suspended  in  water  and  oils,  and  in  this  way  become 
useful  as  a  lubricating  material. 


12  THE:  COLLOIDS  IN  THE  INDUSTRIAL  ARTS 

possible,  by  long  dialysis,  it  does  not  coagulate,  when 
heated,  but  it  does  so  when  salts  are  subsequently  added 
to  it.  Complete  coagulation  ensues  only  when  the  solu- 
tion reacts  slightly  acid.  When  milk,  for  example,  cur- 
dles, proteins  which  have  been  chemically  changed  by 
ferments  are  precipitated ;  the  curdling  represents  an  in- 
termediate step ;  the  curdled  protein  is  completely  coagu- 
lated by  the  subsequent  heating. 

When  the  precipitated  colloid  changes  to  the  form  of 
a  Gel,  it  still  does  not  completely  separate  from  the 
water,  but  forms,  as  I  have  mentioned  before,  a  peculiar 
honey-comb-like  structure,  which  contains  enclosed 
water. 

5.  Reversible  and  Irreversible  States  of  Aggregation. — 

When  pure  hydrosols  of  metals  are  precipitated,  no  real 
Gel- formation  results,  but  a  sort  of  metallic  sponge  is 
produced.  In  the  case  of  precipitated  gold  a  light  pres- 
sure with  the  burnisher  is  sufficient  to  transform  the 
dried  powder  into  coherent  metal.  If  it  should  be  desired 
to  bring  this  gold  again  into  the  condition  of  a  colloidal 
solution,  this  could  be  accomplished  only  in  a  round- 
about way,  probably  by  dissolving  it  in  aqua-regia  and 
reducing  the  solution  with  formaldehyde.  But  colloidal 
silver,  which  is  prepared  by  the  method  of  C.  Lea1  and 

1  C.  Lea  reduces  the  solution  of  silver-nitrate  with  iron  sul- 
phate in  the  presence  of  sodium  citrate. 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  13 

which  contains  organic  impurities,  easily  dissolves  in 
water;  it  can  even  be  precipitated  from  the  colloidal 
(blood-red)  solution  by  ammonium  nitrate,  and  then 
again  dissolved  in  water.  Such  Sols  used  to  be  desig- 
nated as  reversible  (umkehrbar)  and  the  hydrosol  of 
gold  was  considered  as  an  example  of  another  class,  the 
irreversible  Sols.  This  difference  in  behavior  is,  how- 
ever, not  so  much  due  to  the  nature  of  the  respective  sub- 
stance, as  to  the  treatment  which  is  accorded  to  it.  For 
this  reason,  in  a  strict  sense,  it  can  be  spoken  only  of 
reversible  and  non-reversible  states  of  aggregation  of 
the  colloids. 

Colloidal  silicic  acid,  which  in  the  process  of  evapora- 
tion has  lost  but  little  water,  can  be  liquefied  by  an  addi- 
tion of  water ;  even  in  a  somewhat  later  stage  of  the  pro- 
cess of  evaporation  the  silicic  acid  can  be  brought  into 
solution  by  treating  it  with  a  solution  of  caustic  soda; 
according  to  Th.  Graham  one  part  of  sodium  hydroxide 
in  1,000  parts  of  water  is  sufficient  to  convert  into  hydro- 
sol 200  parts  of  silicic  acid  when  the  whole  is  cooked  for 
one  hour.  This  liquefaction  process  used  to  be  termed 
peptisation ;  by  this  term  it  was  compared  with  the 
process  of  transformation  of  protein  into  pepton  which 
goes  on  in  the  intestines  when  food  is  digested. 

Reversible  states  of  aggregation  are  caused  by  change 
of  temperature  in  lime,  agar-agar,  and  fish-glue,  which, 


14  THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS 

when  they  have  a  certain  composition,  congeal  in  the 
cold  to  a  semi-solid  Gel  that  liquefies  again  on  being 
warmed. 

6.  General  Remarks  on  Dispersed  Systems. — The  term 
dispersed  systems,  has  recently  been  introduced  to 
designate  compositions  in  which  one  substance  is  very 
finely  divided  within  another  one.  The  finely  divided 
substance  is  termed  the  dispersed  phase,  while  the 
other,  which  is  mostly  in  very  large  excess,  is  not  termed 
the  "solvent,"  but,  in  a  more  general  way,  the  dispers- 
ing medium.  From  these  dispersed  systems,  which 
come  under  the  term  colloidal  solutions,  are  distinguished, 
on  the  one  hand,  suspensions,  or  aggregated  dispersed 
systems  (grob  disperse,)  and,  on  the  other  hand,  true 
solutions,  or  molecular  dispersed  systems.  A  sharp 
dividing  line  cannot  be  drawn  between  either  of  these 
systems;  in  reality,  all  such  dispersed  phases,  the  par- 
ticles of  which  measure  between  one  ten  thousandth  to 
one  five  hundred  thousandth  of  a  millimeter,  have  to  be 
considered  as  colloidal  solutions. 

The  suspensions  differ  in  their  behavior  from  the  col- 
loidal solutions  in  that  they  can  be  separated  from  the 
solvent  by  sedimentation,  or  more  rapidly,  by  centrifu- 
galizing;  by  stirring  up  the  separated  slime  the  suspen- 
sion is  mostly  restored.  When  filtered,  the  slime  is  re- 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  1$ 

tained  by  the  filter  paper,  while  colloids  usually  pass 
smoothly  through  the  paper. 

From  the  molecular  dispersed  systems,  the  true  solu- 
tions, colloidal  solutions  are  distinguished  in  that  in  re- 
flected light  they  appear  turbid,  and  that  they  exhibit 
the  so-called  Tyndal-.Effect.  If  a  bundle  of  bright  light- 
rays,  condensed  by  lenses  to  a  cone,  is  thrown  (as  in 
an  ultra-microscope)  into  a  colloidal  solution,  thejight- 
cone  shines  with  a  more  or  less  bright  light, 
on  the  size  and  the  reflective-power  of  the 
ticles,  while  a  true  solution,  on  the 
dark.  In  that  special  case,  xvhen  the  true  solution  con- 
tains a  fluorescent  substance,  (for  example,  a  water  ex- 
tract of  chestnut-bark)  it  will,  indeed,  also  emit  light, 
but  this  peculiar  bluish  or  greenish  light  is  not  polarized 
like  that  of  the  Tyndall-effect,  i.  e.,  when  observed 
through  a  Nicol-prism,  it  does  not  change  its  brightness 
on  turning  the  prism.  A  second  very  characteristic 
property  of  colloidal  solutions  is  their  very  small  diffu- 
sion power.  Colloids  cannot  permeate  membranes 
which  let  true  solutions  pass  through;  this  difference 
was  made  use  of  to  purify  the  colloidal  solution  of  silicic 
acid  from  salt  by  dialysis  by  means  of  a  parchment  skin. 
On  account  of  this  great  difference  in  the  diffusion,  it 
is  possible  to  conveniently  examine  the  nature  of,  for 
example,  solutions  of  dyes,  by  pouring  same  on  gelatine : 


16  THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS 

if  the  dye  penetrates  the  gelatine,  there  is  a  true  solution ; 
but  if  the  separating  surface  remains,  then  we  have  a 
colloidal  solution. 

7.  Suspension  and  Emulsion-Colloids. — Lately  the  col- 
loids have  been  very  properly  divided  into  two  classes. 
The  distinction  is  between  those  colloidal  solutions  in 
which  the  finely  divided  substance  is  liquid,  here  the 
dispersed  phase  consists  of  ultra-microscopical  fluid  par- 
ticles, the  emulsion-colloids,  and  those  in  which  the  small 

:          "' 

particles  are  solid,  which  are  termed  suspension-colloids. 
In  the  colloidal  solution  of  gold  we  have  an  excellent 
example  of  the  suspension-colloids,  or  shorter  the  sus- 
pensions. To  the  emulsion-colloids  belong,  in  the  first 
place,  gelatine,  and  protein-solutions.  Suspension-col- 
loids are  flocculated  even  by  a  small  addition  of  an  elec- 
trolyte; emulsion-colloids  are  much  more  stable.  Sus- 
pension-colloids scarcely  influence  the  mobility  of  the 
solvent,  but  emulsion-colloids  make  the  solvent  more  vis- 
cous, and,  in  general,  the  viscosity  (the  internal  friction) 
of  emulsions  increases  very  much  upon  cooling.  These 
differences  disappear  inasmuch  as  they  depend  on  the 
solvent,  and  very  diluted  emulsoids  may  behave  like  sus- 
pensoids,  while  the  latter,  on  the  contrary,  at  higher  con- 
centrations, resemble  the  first.  The  upper  concentration 
limit  of  the  suspensoids  is  mostly  small;  R.  Zsigmondy 
was  able  to  prepare  colloidal  solutions  of  gold  with  the 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  17 

highest  content  of  only  o.i  per  cent,  of  gold,  and  G. 
Bredig  was  able  to  obtain,  by  electrical  spraying,  not 
more  than  0.014  per  cent.  Indeed,  W.  R.  Whitney  and 
J.  C.  Blake  prepared,  in  roundabout  ways,  more  concen- 
trated gold-sols,  but  there  is  no  assurance  that  we  do  not 
have  to  do  in  this  case  with  a  suspension.  Emulsoids 
have  no  upper  limit  of  concentration. 

To  the  emulsions  belong  also  the  foams.  That,  for 
example,  of  the  white  of  an  egg,  which  is  beaten  to  a 
foam,  is  a  mixture  of  two  liquids,  and  does  not  probably 
consist  of  skins  filled  with  liquid.  This  becomes  evident 
when  the  foam  settles  in  the  cold :  it  melts  then  to  a  clear 
solution,  which  can  easily  be  freed  from  the  impurities 
of  the  white  of  an  egg  (threads,  coagulums). 

Common  to  all  colloids  is  the  very  fine  division  and, 
therefore,  the,  in  comparison  with  the  mass,  enormous 
surface-development.1  The  more  the  surface  is  devel- 
oped, the  more  come  into  the  foreground  the  actions  of 
the  surface  energy,  which  endeavor  to  reduce  the  surface, 
and  for  that  purpose  strive  to  clump  the  small  particles 
together  to  a  larger  structure.  On  the  other  hand,  all 

1  The  total  surface  increases  in  the  same  proportion  as  the 
diameter  of  the  separate  particles  decreases.  For  example,  a  clay 
ball  of  one  centimeter  in  diameter  has  a  surface  of  3  square  centi- 
meters (in  round  figures);  if  this  mass  is  divided  into  100,000  little 
balls,  the  total  surface  is  then  equal  to  more  than  30  square  meters. 


1 8  THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS 

bodies  endeavor  to  draw  from  their  surroundings  and 
to  accumulate  on  their  surface  gases,  liquids,  and  solid 
particles.  In  the  colloids,  with  their  very  much  devel- 
oped surface,  this  endeavor,  likewise,  comes  to  the  fore- 
ground. In  the  following  chapters  we  shall  see  of  what 
value  these  general  properties  of  the  colloids  are  to  the 
technics,  and  which  special  part  certain  colloids  play  in 
technical  processes. 

8.  Ruby  Glass. — The  magnificent  color  of  the  colloidal 
solution  of  gold  we  find  reproduced  in  the  gold  ruby 
glass.  Genuine  ruby  glass  is  obtained  when  gold- 
chloride  is  added  to  the  glass-mass.  If  the  mixture  is 
cooled  off  quickly,  a  colorless  glass  is  obtained,  which, 
when  subsequently  heated  to  the  softening-point,  sudden- 
ly becomes  tarnished  by  a  splendid  ruby-red.  The  quan- 
tity of  gold  which  is  contained  in  ruby  glass  is  minute, 
only  0.05  to  0.06  per  cent.  In  the  red  glass  H.  Sieden- 
topf  and  R.  Zsigmondy  were  able  to  distinctly  discern 
the  ultra-microscopical  particles  of  gold.  Their  follow- 
ing experiment  is  very  instructive:  They  heated  to  the 
melting-point  one  end  of  a  strip  of  colorless,  very  slowly 
cooled  ruby-glass,  while  the  other  end  remained  cold. 
The  hot  end  of  the  glass  became  shining  red,  the  red 
coloration  weakening  towards  the  cold  end,  while  the  lat- 
ter unheated  part  of  the  glass  remained  entirely  color- 
less. The  ultra-microscope  showed  in  the  shining  red 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  IQ 

part  of  the  glass  brilliant-green  particles  in  very  short 
distances  from  one  another;  in  the  weakly  red  one  there 
was  but  a  symmetrical  green  light-cone,  which  was  weak- 
ening towards  the  colorless  end. 

When  a  strip  of  poor  ruby-glass  was  heated  in  a 
similar  manner  unilaterally,  its  hot  end  was  colored  blue, 
the  coloration  becoming  weaker  towards  the  cold  end, 
being,  first  violet,  and  then  light  pink,  while  the  cold  end 
again  remained  colorless.  In  this  case  the  ultra-micro- 
scope showed  brighter  single  particles,  which  were  sep- 
arated from  one  another  by  much  longer  distances,  and 
which  shone  copper  red  in  the  blue  part  of  the  glass, 
yellow  further  on,  and  green  in  that  part  of  the  glass 
which  appeared  pink  in  the  transparency.  The  average 
distance  from  one  particle  to  another  was,  however,  as  in 
the  good  ruby-glass,  about  the  same  in  the  entire  strip 
The  brightness  of  the  particles  diminished  from  the  blue 
toward  the  colorless  end ;  in  this  case  feebly  lighted  par- 
ticles could  be  discerned  also  in  the  cold  part  of  the 
strip. 

These  entangled  phenomena  can  be  interpreted  in  the 
following  manner:  On  cooling,  gold  particles  separate, 
which,  however,  are  too  small  to  give  the  glass  any  color- 
ation. These  gold  germs  ( Goldkeime  ) ,  when  heated  again, 
grow  and  produce  the  beautiful  ruby-red;  they  grow 
the  quicker  the  hotter  the  glass,  therefore,  the  time  of 


2O  THE  COLIXHDS  IN  THE  INDUSTRIAL  ARTS 

heating  being  equal,  the  largest  particles  of  gold  are  to 
be  found  in  those  places  which  were  exposed  to  the 
greatest  heat.  This  separating  of  the  gold  can  last  only 
until  the  supersaturation-point  of  the  respective  kind  of 
glass  and  temperature  is  reached. 

Under  the  ordinary  conditions  of  work  only  a  part 
of  the  total  gold  separates  in  the  ruby-glass  as  the  color- 
ing matter  in  the  form  of  ultra-microscopic  particles.1  If 
the  red  ruby-glass  is  remelted  at  a  white  heat,  the  gold 
goes  again  into  solution  and  the  fusion  remains  colorless 
when  cooled,  but  by  reheating  it  may  again  be  colored  red. 

Some  kinds  of  ruby-glass  are  tarnished  red  already 
upon  cooling;  in  these  glasses  the  conditions  for  the 
formation  and  growth  of  crystallization  center-points 
upon  cooling  are  more  favorable. 

The  reason  why  the  edges  of  a  pressed  ruby-glass  re- 
mained colorless  on  heating  are  also  of  interest :  the  edges 
cooled  in  the  press  more  rapidly  and  on  reheating 
warmed  up  more  rapidly  and  hotter  than  the  center.  In 
the  ultra-microscope  the  edges  showed  much  less  but 
considerably  larger  green  particles  of  1 10  to  145  /*/*  than 
the  rest  of  the  glass-mass.  The  edges  had  to  pass 
through  the  temperature  of  the  germ-formation  too 
rapidly,  so  that  only  few  germs  could  develop  which  on 

1  This  has  been  proven  by  colorimetrical  experiments.   See:  R. 
Zsigmondy,  Zur  Erkenntniss  der  Kolloide  (Jena  1905),  pp.  128-135. 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  21 

reheating  rapidly  grew  to  a  considerable  magnitude. 
But  the  center  of  the  glass  upon  cooling  had  enough 
time  to  develop  a  large  number  of  germs  which  on  heating 
were  less  strongly  warmed  and  therefore  did  not  grow 
as  rapidly. 

In  spoiled  ruby-glass  the  germ  formation  and  growth 
are  disturbed;  there  are  less  germs  developed  and  these 
grow  slower  than  in  good  ruby-glass.  R.  Zsigmondy  as- 
sumes that  instead  of  simple  crystals,  crystalline  germs 
were  formed. 

The  coloration  process  in  copper  ruby-glass  may  be 
similar  to  that  in  gold  ruby-glass.  Copper  ruby-glass 
upon  cooling  is  colored  greenish,  and  only  on  being  gently 
heated  it  becomes  red.1 

9.  Milky- White  Opaque  Glass.  Troostite.  Phosphorus. — 

Milky-white  opaque  glass,  which  has  been  prepared  by 
the  addition  of  fluor-spar,  contains,  according  to  A.  Lot- 
termoser,2  calcium  fluoride  in  the  condition  of  a  colloidal 
solution.  The  fact  that  such  glass  appears  turbid  in  re- 

1  H.  Siedentopf  explained  in  a  similar  manner  the  blue  color- 
ation, which  at  times  appears  in  rock  salt.  In  this  case  the  ultra- 
microscopical  crystals  of  metallic  sodium  are  the  coloring  matter. 
H.  Siedentopf  was  able  to  prepare  artificially  such  colored  sodium- 
chloride  crystals,  by  treating  them  in  vacuum  with  vapors  of 
sodium  or  potassium.  When  reheated  the  color  changes,  because 
the  ultra-microscopical  particles  undergo  a  similar  change  as  those 
of  ruby-glass. 

8  A.  Lottermoser,  Zeitschr.  f.  angew.  Chemie,  1906,  19  :  369-377. 


22  THE  COLLOIDS  IN  THE)  INDUSTRIAL  ARTS 

fleeted  light  and  allows  transmitted  light  to  pass  through 
clearly  with  a  yellowish  color,  speaks  in  favor  of  the  ac- 
ceptance of  this  theory.  The  glaze-colorations,  which 
are  formed  by  metals,  may  also  be  considered  as  colloidal 
solutions.1 

Colloidal  solutions  occasionally  appear  also  in  metal- 
alloys.  So,  C.  Benedicks2  considers  the  structural-ele- 
ment (Gefiigebestandtheil)  of  slowly  cooled  steel,  the 
Troostite  (an  intermediate  stage  between  Martensite  and 
Pearlite),  discovered  by  F.  Osmond,  as  a  colloidal  solu- 
tion of  cementite  (iron-carbide).  If  this  Troostite  is 
heated  to  150  degrees  for  a  sufficiently  long  period,  the 
ultra-microscopical  germs  grow  and  needles  of  cementite 
become  visible.3 

Colloidal  intermediate  forms  do  not  seem  to  be  rare  in 
other  transformations.  H.  Siedentopf  found  that  when 
white  phosphorus  changes  into  the  red  form,  a  colloid 
is  obtained  at  first. 

He  observed  that  when  a  piece  of  white  phosphorus 
was  placed  tinder  the  Kardioid-Ultra-microscope  at  a 
magnification  of  1,500  times,  he  noticed  in  the  phos- 

1  Just  as  the  colorations  of  the  borax-  and  sodium-phosphate 
glasses  so  useful  to  the  analyst. 

2  C.  Benedicks,  Zeitschr.  f.  physikal.  Chem.,  1905,  52  :  733. 

3  Sufficient  information  as  to  the  value  of  Martensite,  etc.,  can 
be  found  in  my  book,    "Technische    Anwendungen    der    phy- 
sikalischeu  Chemie"  (Berlin  1907),  p.  235. 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  23 

phorus,  right  after  the  illumination,  small  white  points, 
which  rapidly  grew  to  radiant  brightness,  and  then  turned 
red.  In  a  solution  of  phosphorus  in  carbon  bisulphide 
the  process  is  the  same. 

10.  Colloids  in  the  Mineral  Kingdom. — The  costliest 
members  of  the  mineral  kingdom,  the  precious  stones, 
owe  their  magnificent  color,  often,  to  minute  quantities 
of  a  colloidally  dissolved  coloring  substance.  C.  Doelter 
includes  in  this  class,  among  others,  the  smoky  (yellow) 
topaz  and  most  of  the  sapphires,  the  beautiful  blue  color 
of  which  is  due  to  colloidal  cobalt  oxide;  in  ruby,  how- 
ever, he  assumes  the  coloring  substance  to  be  a  true  solu- 
tion of  chromium  oxide  in  alumina.  A  very  beautiful 
artificial  ruby,  which  belongs  to  me,  appears  indeed 
in  reflected  light  turbid  and  dark,  just  like  a  colloidal 
solution  of  gold  on  heating,  it  turns  green;  upon  cooling 
it  is  again  colored  red. 

Of  the  semi-precious  stones,  the  opal  is  to  be  consid- 
ered as  a  colloid,  and  in  fact  as  a  Gel.  According  to  F. 
Cornu,1  the  Gels  are  in  general  far  more  numerously 
represented  in  minerals  than  was  hitherto  supposed ;  they 
are  the  typical  products  of  all  normal  disintegration  pro- 
cesses. So,  for  example,  bauxite  (aluminium-hydrox- 
ide) and  the  already  mentioned  opal  (hydrated  silica) 
are  such  colloidal  products  of  the  disintegration  of 

1  F.  Cornu,  Koll-Zeitschr.,  1909,  4  :  15,  and  in  other  places. 
3 


24  THE:  COLLOIDS  IN  THE:  INDUSTRIAL  ARTS 

rocks.  Numerous  Gels  appear  also  in  the  oxidation  zone 
of  the  ore-beds,  for  example,  Psilomelane  in  the  man- 
ganese  ores.  The  Gels  of  the  mineral  kingdom  are  dis- 
tributed, according  to  F.  Cornu,  in  the  groups  of  the 
hydroxides,  the  sulphates,  the  hydrated  phosphates,  the 
arsenates,  the  antimonates  (Bleiniere),  the  silicates,  and 
the  salts,  which  contain  organic  acids  (Dopplerite  of  the 
moss-worts)  ;  they  are  entirely  absent  in  the  other  groups, 
for  example,  in  the  sulphides,  the  carbonates,  and  the 
anhydrous  silicates,  etc. ;  that,  indeed,  is  to  be  expected, 
if  the  mode  of  their  formation  as  disintegration  products 
is  taken  into  consideration. 

The  external  characteristic  of  the  mineral  Gels  is  the 
conchoidal  fracture,  presupposing  that  they  have  not 
lost  any  water;  they  often  stick  to  the  tongue. 

Many  mineral  colloids  have  their  crystalline  antitypes. 
So,  for  example,  opal  has  an  antitype  in  Calcedony, 
which  appears  as  a  crystalline  transformation  product  of 
the  colloidal  form. 

As  especially  important  colloids  of  the  mineral  king- 
dom, I  will  also  mention  kaolin,  anthracite  and  bog-iron- 
ore. 

In  the  soil  there  are  present  in  the  form  of  colloids 
iron  oxide,  silicic  acid,  amorphous  silicates,  and  the 
humus  substances;  as  non-colloidal  ingredients  there 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  25 

are  quartz,  fragments  of  crystalline  silicates,  and  the 
simple  salts,  such  as  calcium  carbonate,  phosphates, 
chlorides,  and  sulphates.  The  humus  substances  form 
an  amorphous  complex  of  decomposition  products  of  the 
sugars  and  proteins;  they  are  agglomerated  with  the 
colloidal  silicates  and  adhere  also  to  the  crystalline  par- 
ticles.1 

11.  Silver  and  Gold  Mirrors. — The  flocculation  of  hy- 
drosols  of  metals  is  made  use  of  in  the  preparation  of 
silver  and  gold  mirrors  on  glass.  Under  certain  con- 
ditions, the  silver  separates  from  the  colloidal  solution 
on  the  glass  plate  as  a  brilliant  mirror.  The  whole  pro- 
cess lasts  few  or  several  minutes,  according  to  which 
formula  is  employed  in  the  preparation  of  the  silver- 
mirror  (all  are  based  on  the  reduction  of  a  silver  salt  in 
a  dilute  solution  by  formaldehyde,  sugar,  or  Seignette- 
salt,  etc.) ;  as  an  intermediate  stage  there  appears  a 
brick- red  colloidal  solution  of  silver.  If  the  process  is 
conducted  incorrectly,  instead  of  a  coherent  brilliant 
metallic  layer,  a  grayish-yellow  skin  and  a  slimy  or  gran- 
ulated powder  separate.  The  fact,  that  the  slightest  de- 
viation from  the  formula  is  so  fatal,  is  not  surprising 
if  the  sensitiveness  of  colloidal  solutions  is  taken  into  con- 
sideration. As  it  is  well  known,  the  preparation  of  the 
glass,  which  is  to  be  silvered,  is  also  important;  the  sep- 
1  Gedenkboek,  J.  M.  van  Bemmeln  (Haider),  1910,  p.  62. 


26  THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS 

aration  is  facilitated  if  the  surface  is  already  overlayed 
by  a  silver  coating,  even  if  this  is  an  invisible  one.  In 
the  analogous  process  of  gilding  the  preliminary  pro- 
duction of  an  invisible  gold  layer  is  even  necessary.  The 
ultra-microscopical  particles  rapidly  attach  themselves 
to  the  already  separated  metallic  particles.  The  metallic 
mirror  can  be  reinforced  as  desired  by  the  addition  of 
a  fresh  quantity  of  the  colloidal  solution. 

Since  the  silver-mirror,  in  spite  of  its  exceedingly 
small  thickness,  is  a  good  conductor  of  the  electrical  cur- 
rent, it  is  possible  to  electro-deposit  on  it  a  thick  layer 
of  copper  and  then  on  the  latter  a  thin  layer  of  palladium. 
S.  Cowper-Coles  manufactures  hollow  metallic  mirrors 
on  a  large  scale  by  producing  them  on  curved  glass- 
molds  in  the  way  described,  and  then  separating  the 
metallic  layer  by  heating. 

12.  Manufacture  of  Tungsten  Lamps. — While  in  the 
preparation  of  metallic  mirrors  the  separation  of  the  col- 
loid in  the  form  of  a  coherent  metallic  layer  is  desired, 
and  that  part  which  is  flocculated  as  an  invisible  powder, 
is  considered  as  an  inconvenient  waste;  in  the  manufac- 
ture of  tungsten  lamps,  on  the  contrary,  we  desire  to 
obtain  the  metal  in  the  form  of  a  Gel,  because  this  Gel 
is  sufficiently  plastic  to  be  pressed  into  thin  filaments. 
One  would  wonder  why  the  compact  tungsten  metal  is 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  2/ 

not  rolled  out  and  squirted  into  filaments  directly,  as  it 
is  done  with  the  tantalum  metal  for  tantalum-lamps.  Un- 
fortunately, metallic  tungsten  is  much  too  brittle  to  be 
drawn  into  wire,  not  to  mention  filaments  of  less  than 
0.05  millimeter  in  diameter,  as  those  that  are  used  as 
metallic  filaments  in  incandescent  lamps.1  On  the  other 
hand,  tungsten,  which  melts  only  at  about  2,900°  (1,000° 
higher  than  platinum  and  500°  higher  than  tantalum), 
by  the  reason  of  its  cheapness,  is  especially  fitted  for 
the  preparation  of  filaments  for  lamps  on  account  of  its 
exceedingly  high  melting-point.  The  aspiration  of  the 
lighting  industry  is  concentrated  in  an  endeavor  to  heat 
the  illuminative  body  to  the  highest  temperature  possible, 
because  the  light-radiation  increases  extraordinarily  rap- 
idly with  the  increase  of  temperature.  The  higher  the 
temperature  of  the  illuminative  body,  the  larger  the  part 
of  energy,  with  which  it  is  supplied,  is  transformed  into 
light.  Carbon,  indeed,  does  not  melt,  but  the  carbon 
filament,  in  general,  cannot  be  heated  over  1,800  degrees 
without  deteriorating.  The  metallic  filament  lamps  are 
able  to  glow  so  much  brighter,  since  such  lamps  consume 
for  each  normal  candle-power  only  about  one  volt,  i.  e., 

1  The  metals  are  better  conductors  than  carbon  ;  for  that  rea- 
son the  lamps,  which  are  intended  for  the  use  with  the  current  of 
the  usual  pressure  of  1 10  volts  require  long  metallic  filaments,  in 
order  to  furnish  the  necessary  electrical  resistance. 


28  THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS 

only  about  one-third  of  the  electrical  energy,  which  is 
consumed  by  the  old  carbon  filament  lamps. 

The  filaments  for  osmium  lamps,  made  from  metallic 
osmium,  which  cannot  be  drawn  into  threads,  can  be 
prepared  in  a  chemical  way,  by  igniting  carbon  threads  in 
an  atmosphere  of  the  vapors  of  osmic  acid,  a  very  vola- 
tile oxygen  compound  of  osmium.  At  this  high  heat, 
the  osmic  acid  is  decomposed  into  osmium  and  oxygen, 
the  osmium  is  deposited  on  the  thread,  while  the  carbon 
and  oxygen  burn  off,  so  that  a  thread  of  metallic  osmium 
results  at  last. 

The  common  method,  however,  was  to  pulverize  the 
metal,  as  finely  as  possible,  mix  it  with  a  binding  material, 
such  as  dextrin,  gum-solution,  sugar-syrup,  to  a  thick 
mush  and  squirt  this  under  high  pressure  through  fine 
holes  to  form  filaments  of  the  desired  thickness  and  form. 
These  filaments  were  heated  strongly,  whereby  the  or- 
ganic binding  material  was  carbonized ;  in  this  way  fused 
filaments  were  obtained,  which  conducted  well  and  which 
contained  the  carbon  in  the  form  of  carbide  or  as  a 
solid  solution. 

The  same  methods  can  also  be  applied  to  tungsten, 
when  either  the  volatile  tungsten-oxy-chloride  is  em- 
ployed, or  the  pulverized  tungsten  is  worked  to  a  dough 
with  some  binding  material.  But  the  second  method, 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  2Q 

which  hitherto  was  employed  by  preference,  has  its  de- 
fects. The  squirting  requires  very  high  pressure  and, 
further,  the  carbon  in  the  finished  filament  is  often  un- 
equally distributed  and  forms  knots;  the  cross-section 
of  the  filament  is  in  other  ways  also  not  uniform  through- 
out the  whole  length.  The  thin  section  offers  to  the  cur- 
rent more  resistance,  is  heated  stronger,  and,  in  conse- 
quence soon  burns  through.1  Binding  materials  were 
tried  which  volatilize  at  moderate  temperatures,  for  ex- 
ample, paraffin  and  camphor  mixed  with  alcohol.  Fin- 
ally H.  Kuzel  has  given  up  the  use  of  any  artificial  bind- 
ing materials  and  made  the  tungsten  extraordinarily 
plastic  in  the  way  indicated  above,  by  converting  it  into 
the  form  of  a  Gel.  The  above  mentioned  binding  ma- 
terials are,  indeed,  themselves  colloids.  If  the  tungsten 
metal  is  pulverized  very  finely  in  a  ball-mill  and  is  pul- 
verized further  again  and  again  for  weeks  and  months,  a 
powder  is  obtained,  which,  being  mixed  with  water,  gives 
a  ductile  mass.  But,  when  this  mass  is  pressed  to  thin 
filaments  in  a  stamping  press,  it  is  noticed  that  the  ductil- 
ity of  the  mass  is  not  yet  sufficient,  that  the  filaments 
break;  they  are  too  brittle  for  further  treatment.  It  is 

1  More  information  can  be  found  in  the  valuable  article  of  A. 
Lottermoser  :  Einige  Bemerkungen  ueber  die  Herstellung  von 
Metallfaeden  fuer  elektrische  Gluehlampen,  besonders  aus  kolloid- 
en  Metallen,  Chem.  Ztg.,  1908:311-313.  See  also  Roll. -Zeitshr., 
1908  :  2,  347. 


30  THE:  COLLOIDS  IN  THE  INDUSTRIAL  ARTS 

possible,  however,  to  bring  the  mechanically  extraordin- 
arily pulverized  tungsten  into  the  colloidal  condition,  in 
fact,  into  a  comparatively  concentrated  solution,  by 
treating  it  alternately  with  alkalies  and  acids,  and  giving 
it,  intermediately,  plentiful  washing.  If  the  tungsten  is 
precipitated  from  this  solution,  a  viscous  mass  of  an  ex- 
ceedingly fine  division  is  obtained,  which  has  all  the  de- 
sirable properties,  and  which  can  be  drawn  out  to  fila- 
ments of  0.03  millimeters  in  cross-section,  through  very 
fine  holes  bored  in  rubies,  without  the  use  of  great  power. 

At  first,  these  filaments  conduct  the  current  badly, 
but  the  small  current,  which  passes  through  them,  is  suf- 
ficient to  heat  the  filament.  In  the  heat  the  small  par- 
ticles combine  to  larger  ones;  the  filament  allows  a 
stronger  current  to  pass  through  and  at  last  at  a  white 
heat  the  tungsten  fuses  to  a  solid,  good  conducting  metal- 
lic filament,  which  meets  all  the  requirements  in  mechan- 
ical and  electrical  respects. 

Instead  of  gradually  heating  the  unfinished  filament 
by  the  electrical  current  in  the  lamp,  the  filaments,  as 
they  come  from  the  press,  and  after  they  are  dried,  are, 
preferably,  ignited  in  an  atmosphere  of  nitrogen,  or  in 
vacuo  (because  the  ignited  tungsten  is  oxidized  by  the 
oxygen  of  the  air).  The  desired  metallic  filaments  are 
at  last  obtained  at  a  white  heat.  They  are  then  cut  into 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  31 

the  proper  length,  and  are  cemented  to  the  current-lead- 
ing-in-wires  in  the  lamp  socket  by  means  of  tungsten 
Gel;  by  heating  also  this  cement  is  transformed  into  a 
coherent  metal.  After  that  the  glass  globe  is  placed  over 
the  filaments  and  fastened  to  the  socket,  finally  the  lamp 
is  evacuated,  or  filled  with  nitrogen  gas,  and  sealed. 
The  siriuscolloid  lamps,  which  are  manufactured  in 
Germany  by  J.  Pintsch,  are  claimed  to  withstand  a  cur- 
rent of  considerable  overpressure,  without  being  deter- 
iorated. 

The  Auer-Gesellschaft  manufactures  its  osra-lamps 
by  a  different  process,  the  details  of  which  have  not  been 
made  public. 

With  reference  to  the  theoretical  explanation  of  the 
Kuzel  process,  A.  Lottermoser  assumes  that  the  grains 
of  the  already  exceedingly  fine  ground  tungsten  powder 
are  etched  by  the  alternating  treatment  with  alkalies  and 
acids,  and  in  this  way  they  are  finally  reduced  to  the 
diameter  of  ultra-microscopical  particles.  Further,  the 
chemicals  applied  in  this  process  introduce  into  the  solu- 
tion certain  ions  which  make  the  metal-hydrosol  stable 
when  they  are  present  in  a  definite  small  concentration 
(for  this  reason  the  plentiful  washings  between  the  sep- 
arate etchings  are  employed)  ;  these  ions  are,  probably, 


32  THE:  COLLOIDS  IN  THE  INDUSTRIAL  ARTS 

the  hydrogen-ions  of  the  acids,  on  the  one  hand,  and  the 
hydroxyl-ions  of  the  alkalies,  on  the  other  hand.1 

It  has  been  found  lately  that  perfectly  pure  tungsten 
is  ductile  and  can  be  drawn  out  to  threads  of  1/50  mil- 
limeter thickness,  such  as  are  used  in  metal-filament 
lamps.  This  discovery  will,  probably,  overturn  the  whole 
industry,  and  will  do  away  with  colloidal  tungsten. 

13.  Colloids  in  the  Ceramic  Industry. — As  in  the 
younger  tungsten-lamp  industry,  so,  from  ancient  times, 
in  the  ceramic  industry  the  Gel  formation  is  utilized  in 
order  to  make  the  pliant  ceramic  mass  more  plastic.  The 
noblest  material  of  the  ceramic  industry,  porcelain  clay, 
which  consists  of  almost  pure  aluminium  silicate,  is  first 
freed  from  the  heavier  and  coarser  particles  by  very 
careful  washing,  and  is  then  mixed  with  "diluting-mater- 
ials"  (Magerungsmitteln),  Feldspar  and  quartz,  which 
are  also  very  finely  ground  and  washed.  In  spite  of  the 
painful  mechanical  preparation,  this  mass,  after  being 
freed  from  the  superfluous  water  in  a  filter-press  and 
wedged  in  a  wedging  machine,  is,  (like  the  powdered 
tungsten),  not  yet  sufficiently  plastic  to  be  subjected  to 
further  treatment  at  once;  it  must  be  previously  stored 
for  a  long  period.  During  the  storing  in  a  damp  cellar 
the  porcelain  mass  becomes  black  and  evolves  gases,  car- 
bonic acid,  ammonia,  hydrogen-sulphide,  which  originate 
1  A.  Lottermoser,  loc.  cit. 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  33 

in  the  decomposed  organic  ingredients  that  were  intro- 
duced into  it  partly  by  the  raw  materials,  partly  by  the 
water.1  This  process  is  termed  "mellowing/'  or  "cur- 
ing" (Faulen,  Mauken).  The  longer  the  mass  is  mellow- 
ing the  more  pliant  it  becomes ;  usually  the  mass  is  stored 
at  least  for  three  months.  According  to  P.  Rohland  the 
success  of  the  mellowing  consists  in  the  formation  of 
a  colloid  which  is  peptised  under  the  influence  of  the 
alkali  present  in  the  mass.  The  acid  fermentation  of  the 
organic  substances  causes  the  binding  of  the  alkali  and 
therewith  the  coagulation  of  the  colloidal  solution. 

Kaolin  also,  which  is  by  itself  more  plastic  than  the 
porcelain  mass,  must  be  mellowed  previous  to  being  sub- 
jected to  further  treatment. 

A  very  interesting  application  of  the  peptisation  of 
the  colloids  is  the  process,  discovered  by  E.  Weber  for 
the  manufacture  of  glass  melting-pots  by  casting.  By 
the  addition,  according  to  the  nature  of  the  fire-resistant 
clay,  of  a  small,  accurately  measured,  quantity  of  soda 
and  a  little  water,  under  constant  vigorous  stirring,  he 
transforms  the  finely  ground  slip  into  a  thin  mush,  which 
is  then  run  out  from  the  mixing  vessel  into  the  pot  molds 
placed  below.  If  the  slip  were  mixed  with  water  only, 
it  would  soon  settle  to  the  bottom  of  the  mold,  while 
in  the  Weber's  process  the  whole  mush  gradually  hard- 
1  R.  Dietz,  Das  Porcellan  (Halle),  1907  :  41. 


34  THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS 

ens  to  a  solid  mass,  which  is  uniform  in  structure  and 
thick  in  the  fracture,  for  which  reason  the  pots  do  not 
suffer  any  longitudinal  cracks,  even  at  more  considerable 
fluctuations  of  temperature  in  the  glass  furnace. 

Besides  the  greater  durability  in  comparison  with  the 
pots  which  were  formed  by  hands,  the  casting  process 
means  also  a  considerable  saving  in  time  and  labor.  The 
production  of  one  pot,  which  holds  220  to  225  kilograms 
of  glass,  requires  from  the  time  when  the  mixture  is 
measured  up  to  the  time  when  the  filled  mold  is  carried 
away  not  more  than  one  hour.  After  24  hours  of  stand- 
ing still  the  pot  has  hardened  so  much  that  the  core  of 
the  mold  can  be  taken  out;  after  a  further  24  hours  the 
mantel  is  taken  off  and  at  the  same  time  the  upper  edge 
of  the  casting  is  cut  off.  Further  treatment  is  not  re- 
quired. This  process  has  been  employed  since  1905  in 
the  glass  works  of  Aug.  Leonhardi  in  Schwepnitz  (Sax- 
ony). 

Clays,  which  cannot  be  liquefied  by  soda  only,  as  J. 
Keppeler1  found,  can  be  brought  into  that  condition  by 
the  addition  of  humic  acid. 

In  drying  in  the  kiln  the  colloidal  ingredients  distin- 
guish themselves  in  that  they,  in  correspondence  with 
their  large  surface  development,  tend  in  a  large  measure 

1  See  the  lecture  by  J.  Keppeler,  Zeitschr.  f .  angew.  Chemie, 
1909,  22  :  526. 


THE  COLLOIDS  IN  THE  INDUSTRIAL   ARTS  35 

to  diminish  their  surface  by  shrinking.  Crystalline  sub- 
stances do  not  manifest  such  fire-shrinking  properties  at 
all.  Due  to  the  fine  division  of  their  mass,  the  colloids 
are  usually  at  the  head  also  in  respect  to  the  rapidity  with 
which  they  change  into  other  states  of  aggregation. 
While,  for  example,  quartz  crystals,  even  at  a  white 
heat  change  but  very  slowly  into  the  crystalline  form, 
tridymit,  which  is  stable  at  temperatures  above  1,000 
degrees,  and  also  quartz-glass  transforms  only  slowly, 
the  colloidal  silicic  acid  forms  tridymit  rapidly  even  at 
1,000  degrees. 

14.  Colloids  in  the  Hydraulic- Cement  Industry. — Just 
as,  according  to  the  theory  of  P.  Rohland,  in  kaolin  and 
porcelain,  so  also  in  cement  does  the  colloidal  condition 
play  an  important  part. 

According  to  W.  Michaelis1  in  the  first  stage  of  the 
hardening  process  of  Portland  cement,  in  that  stage, 
which  is  called  setting  (Abbinden),  there  are  formed, 
with  absorption  of  water,  colloidal  calcium  hydro-silicate 
and  -aluminate,  and  colloidal  calcium  hydroxide.  The 
crystals  of  calcium  hydroxide  and  calcium  aluminate, 
which  are  formed  gradually,  find  in  the  yielding,  jelly- 
like  colloid-mixture  room  for  their  development;  in 
separating  out  these  crystals  petrify  more  and  more  the 

1  W.   Michaelis,    Jahresbericht  der  chemischen  Technology, 
1906  :  109,  ff. 


36  TH£  COLLOIDS  IN  THE  INDUSTRIAL  ARTS 

first  perfectly  elastic  colloid,  which,  moreover,  on  drying 
becomes  by  itself  hard  as  a  stone,  thus  cementing  by  it- 
self the  sand-grains  or  the  crystals,  which  are  embedded 
in  it.  The  colloidal  cement,  this  "mineral  Gel,"  as  W. 
Michaelis  calls  it,  protects  the  iron  in  the  iron-ore-cement 
from  rusting,  by  surrounding  it  in  the  form  of  a  thick 
protecting  layer.  The  hardening  of  the  hydraulic  ce- 
ment is  based  on  the  gradual  setting  free  of  the  swelling 
water,  the  continued  hardening  of  the  colloids,  the  bind- 
ing of  water  as  water  of  crystallization,  and  the  continued 
formation  of  crystals  of  calcium  hydroxide.  The  larger 
cement  grains  are  protected  from  the  absorption  of 
water  by  the  jelly-like  calcium -hydro-silicate  and  calcium- 
hydro-aluminate,  which  are  not  permeable  to  water,  so 
that  when  a  pure  cement,  which  has  hardened  under 
water  years  ago,  is  pulverized,  it  hardens  anew  and,  in- 
deed, the  more,  the  coarser  the  original  powder  was. 
Thus,  in  the  hardening  of  the  cement,  we  have  to  do  with 
the  combined  action  of  colloidal  and  crystalline  sub- 
stances; the  water,  which  is  contained  in  the  colloid, 
compels  us  to  make  additions  of  "diluting-materials" 
(Magerungs-mitteln)  in  order,  that  the  cement  on  hard- 
ening, may  not  shrink  too  much. 

E.  Stern,1  indeed,  does  not  accept  this  theory  wholly, 
but  also  thinks  that  the  formation  of  jelly-like  substances 
1  Chem.  Ztg.,  1908  :  85. 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  37 

in  the  period  of  the  setting  of  the  cement  is  very  prob- 
able. To  prove  the  presence  of  colloids,  he  carried  out 
the  following  experiment:  when  hydraulic  cement  (or  a 
pure  aluminate)  is  mixed  up  with  water,  the  lime  and 
alumina  go  into  solution.  If  a  finely  pulverized  alumin- 
ate is  dialysed,  in  the  dialysate  can  be  found  only  lime, 
alumina  is  not  found  at  all,  or  is  present  in  traces  only. 

E.  Stern  studied  the  setting  and  hardening  processes 
more  closely  under  the  microscope,  retarding  these  pro- 
cesses by  the  addition  of  gelatin.  He  spread  coarse- 
grained cement  on  the  object-plate  and  covered  it  with 
a  few  cubic  centimeters  of  a  two  per  cent,  solution  of 
gelatine.  After  drying,  the  gelatine  preparation  was 
immersed  in  water  (100  cc.).  At  the  end  of  24  hours 
the  cement  grains  were  superfically  attacked  by  the 
water,  but  no  crystals  were  to  be  seen  there;  the  larger 
part  of  the  lime  had  diffused  out,  while  aluminium  hy- 
droxide and  calcium  carbonate  were  formed,  which  sur- 
rounded the  cement  grains.  When  the  access  of  air  was 
perfectly  excluded,  instead  of  carbonate,  crystals  of 
calcium  hydroxide  were  formed. 

According  to  Stern,  the  cement  grains,  in  setting,  are 
surrounded  by  a  colloidal  layer;  in  hardening,  crystals 
(sodium  carbonate  and  hydroxide,  aluminate  and  sili- 
cate) separate  out  and,  indeed,  in  the  interior  of  the  ce- 


38  THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS 

merit  block  chiefly  calcium  hydroxide,  and  on  the  exter- 
nal part — calcium  carbonate. 

According  to  P.  Rohland,  the  colloids  are  of  especial 
importance  in  the  hardening  of  cement  in  sea-water, 
because  they  are  impermeable  to  all  salts  of  magnesium, 
which  would  be  detrimental  to  the  mortar. 

15.  Colloids  as  Adhesives  and  Glues. — According  to  the 
above  given  explanation,  we  may  consider  the  colloidal 
elementary  mass  of  the  hydraulic  cement  as  a  binding 
material.  In  a  very  general  way  the  colloids,  indeed, 
are  employed  for  glueing  and  cementing  purposes. 
While  in  soldering  the  liquid  solder  forms  an  alloy  with 
the  metallic  thread  which  is  to  be  soldered,  in  glueing 
such  a  mutual  dissolving  process  does  not  take  place, 
but,  so  to  say,  intimate  interlacing  of  two  cell-structures 
is  produced.  In  glueing  of  wood  and  other  substances 
of  a  cellular  structure,  the  glue,  owing  to  its  great  plas- 
ticity, penetrates  the  pores  of  the  wood  and  on  solidify- 
ing unites  well  glued  pieces  with  such  force  that  they 
can  be  separated  only  with  great  trouble  and  damage. 
Being  interposed  between  flat  surfaces  such  as  metallic 
and  glass,  the  glue  fills  up  the  slightest  depressions  and 
cracks,  even  if  such  are  not  visible  to  the  naked  eye;  in 
this  way  it  forms  in  a  manner,  a  uniform  whole. 

If  the  adhesive  power,  as  it  is  often  assumed,  were 
the  result  only  of  the  elimination  of  all  the  air  between 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  39 

the  two  surfaces,  which  are  glued  together,  and  the  air 
pressure  alone  were  holding  these  surfaces  together,  then, 
first,  the  adhesive  would  bind  best  only  as  long  as  it  re- 
mains moist;  adhesives,  however,  bind  well  only  on  dry- 
ing, and  many  of  these  attain  their  full  adhesive  power 
only  after  a  long  period.  Second,  the  adhesive  power 
could  not  be  any  greater  than  that  which  corresponds  to 
the  air  pressure,  i.  e.,  one  kilogram  to  each  square  centi- 
meter of  the  surface  to  be  glued ;  but  it  is  usually  several 
times  greater.  For  instance,  the  adhesive  strength  of 
good  joiner's  glue  is  150  kg.  to  I  sq.  cm.1  Prom  this 
example  we  may  see  how  great  a  tensile  strength  may  be 
manifested  by  this  delicate  colloidal  structure. 

16.  Usefulness  of  the  Colloids  in  the  Absorption  of 
Liquids. — In  consequence  of  their  peculiar  porosity  the 
colloids  are  able  to  absorb  large  quantities  of  liquids  and, 
indeed,  often,  by  being  swelled  at  the  same  time,  much 
more  than  the  original  volume  of  their  pores.  The 
absorption-ability  is  made  use  of,  for  example  in  electro- 
technics  in  the  preparation  of  dry  batteries;  besides 
plaster  of  Paris,  gelatine,  agar-agar,  blotting-paper, 
saw-dust,  cellulose,  cotton  and  other  organic  substances 
are  used ;  of  the  inorganic  colloids,  in  the  case  of  acidic 

1  See  F.   Knieger,  Kleben  und  Klebbstoffe,  Verhandlungen 
des  Vereins  zur  Befoerderung  des  Geverbefleisses,  1905  :  132. 
4 


4O  THE  COLLOIDS  IN  THE:  INDUSTRIAL  ARTS 

liquids,  the  Gel  of  the  silicic  acid,  and  in  the  case  of 
alkaline  liquids,  iron-oxy-hydrate  are  used. 

This  absorption  power  of  the  colloids  is  also  made 
use  of  in  order  to  remove  disagreeable  liquids ;  Peat- 
molds  (Torf-mull),  for  example,  are  readily  employed 
for  the  absorption  of  liquid  fecal  matters. 

This  water  absorption  plays  an  important  part  also 
in  nature.  The  richer  a  soil  is  in  colloidal  ingredients, 
the  more  water  it  is  able  to  retain.  Cultivated  peat  soil, 
for  example,  which  is  superficially  dried  and  is  still  some- 
what moist  to  the  touch,  contains,  according  to  the  deter- 
minations of  P.  Khrenberg  and  H.  Pick,1  no  per  cent, 
of  the  weight  of  the  dry  substances  in  water;  in  humic 
garden  soil  (fresh  and  moist)  it  is  38  per  cent. ; In  air 
dried,  ground  Dollart-clammy-soil  it  is  1 1  per  cent. ;  in  air 
dried  loess  it  is  3  per  cent.;  and  in  fine  sand  (containing 
0.3  per  cent,  of  organic  substances)  it  is,  according  to 
my  own  determinations,  but  0.2  per  cent. 

17.  Dehydration    of    Peat    by    Electro-Osmosis. — The 

large  quantity  of  liquid  which  is  absorbed  by  peat  is  a 
great  obstruction  to  its  employment  as  a  fuel.  Simple 
pressing  removes  the  water  from  the  peat  just  as  inef- 
fectively as  it  does  from,  for  example,  the  Gel  of  silicic 
acid.  If  it  is  not  desired  to  leave  to  the  air  and  sun  the 
1  Gedenkboek,  J.  M.  van  Bemmeln  (Helder  1910),  pp.  201-204. 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  4! 

tedious  job  of  drying  the  peat,  and  it  is  attempted  to 
evaporate  the  water  ballast  rapidly  by  heating,  one  ex- 
periences difficulties  due  to  the  comparatively  high  cost 
of  this  process.  Several  years  ago  a  process  for  the 
dehydration  of  peat,  which  was  invented  by  Prince 
Botho  Schwerin  drew  considerable  attention;  it  is  based 
on  the  following :  an  electrical  current  of  several  hundred 
Volts  pressure  is  conducted  through  a  thick  mush  of 
ground  peat  and  water;  the  peat  is  then  forced  towards 
the  positive  pole  and  the  water  towards  the  negative  one ; 
in  this  interesting  way  he  succeeded  in  removing  from 
the  peat-slime  a  good  portion  of  its  water. 

18.  Colloids  as  Diaphragms  and  Filters. — The  applica- 
tion of  the  Gels  as  porous  "diaphragms"  and  as  filters  is 
based  on  the  cell  structure  of  the  Gels.  Water,  and 
substances  which  are  really  dissolved  in  water,  pass 
through  the  pores  without  great  difficulty,  but  colloids 
diffuse  only  very  slowly,  or  not  at  all.1  In  nature,  such 
colloidal  diaphragms  are  the  cell-walls  of  plants.  Their 
impermeability  toward  colloids  is  made  use  of  in  the  beet- 
sugar  manufacture,  in  the  process  of  leaching  the  beet 
slices,  the  sugar  passes  out  while  the  colloidal  ingred- 
ients of  the  cell-juice  remain.  Of  the  artificial  dia- 

1  The  diffusion  appears  to  go  on  mainly  through  the  liquid, 
which  is  present  between  the  cell-walls,  while  the  walls  them- 
selves do  not  allow  any  passage. 


42  THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS 

phragms  we  have  mentioned  parchment  paper,  which  is 
employed  in  the  dialysis  of  the  Sols  of  silicic  acid.  On 
the  other  hand,  how  great  the  permeability  is  in  the  case 
of  electrolytes,  is  illustrated,  for  example,  by  the  follow- 
ing: In  storage  batteries  diaphragms  are  sometimes 
used  made  from  sulphite-cellulose  pasteboard.  In  order 
to  make  them  more  durable,  these  diaphragms  are  soaked 
in  rosin.  In  a  short  time,  after  they  are  immersed  in 
the  storage  battery,  these  diaphragms,  in  spite  of  the  fact, 
that  they  have  been  soaked  with  the  non-conducting 
rosin,  absorb  so  much  of  the  sulphuric  acid,  that  they 
conduct  the  current  very  well. 

When  the  particles  of  the  colloidal  solution  are  very 
small,  they  also  will  go  through  very  fine  filters.  Usual 
filter  paper  still  retains  particles  measuring  about  5  /*; 
hardened  filters  permit  the  passage  of  particles  measur- 
ing up  to  2  ju,  and  Pukal-filter-candles,  indeed,  only  up 
to  0.3  /u.  If  the  pores  of  a  filter  paper  are  made  smaller 
by  the  addition  of  jellies  of  different  concentrations,  ac- 
cording to  the  process  of  H.  Bechhold,  a  mixture  of 
different  colloids  may  be  subjected  to  fractional  filtration, 
and  for  example,  colloidal  silver  (Lysargin)  may  be 
separated  from  Haemoglobin  (the  coloring  ingredient  of 
blood). 

19.  Adsorption. — It  is  incorrect  to  consider  the  process 
of  filtration  only  as  a  kind  of  percolation ;  here  comes  to 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  43 

the  foreground  another  property  of  the  colloids,  based 
on  their  cell  structure,  namely,  the  adsorption-power, 
which  is  based  on  their  enormous  surface  development. 
By  the  name  adsorption  is  designated  the  remarkable 
phenomenon  that  gases,  liquids,  and  finely  divided  sub- 
stances adhere,  often  with  great  force,  to  the  surface  of 
many  materials.  Each  window  pane,  for  example,  is 
covered  with  a  not  insignificant  layer  of  water  and  gases, 
from  which  it  can  be  completely  freed  only  by  heating 
for  several  hours  in  an  evacuated  room.  The  adsorption 
power  increases  with  the  surface  and  depends,  not  only 
on  the  nature  of  the  adsorbing,  but  also  on  the  nature  of 
the.  adsorbed  substance.  Colloids  are  preferably  ad- 
sorbed again  by  colloids.  So,  for  example,  the  ultra- 
microscopical  particles  of  gold,  despite  their  small  size, 
are  retained,  in  filtering,  by  the  filter  and  clog  up  the 
pores. 

How  peculiarly  adsorption  acts  can  be  seen,  for  ex- 
ample, in  the  fact  that  R.  Zsigmondy  was  able  to  prevent 
adsorption  on  the  filter  by  adding  white  of  an  egg,  or 
another  protective  colloid,  to  the  hydrosol  of  gold;  gold 
particles  measuring  30  ^  smoothly  passed  through 
Maassen-filter-candles  and  Pukal-filters.  In  this  case 
probably,  also  chemical  combinations  assert  themselves. 
The  usual  proteins,  in  general,  appear  to  be  quite  indif- 


44          THE;  COIXOIDS  IN  THE  INDUSTRIAL  ARTS 

ferent  to  the  material  of  the  filter,  while  ferments  and 
toxins  enter  into  combination  with  it. 

20.  Varnish-Making. — Varnish-making  is  largely  based 
on  the  adsorption  properties  of  the  colloids.     Just  as 
freshly  precipitated  aluminium-hydroxide  takes  up  the 
gold  from  a  colloidal  solution  of  gold  and  produces  a 
beautiful  red  varnish,  so  the  Gel  of  aluminium-hydrox- 
ide causes  other  coloring  matters  to  adhere  to  it.     The 
well-known  receipt  for  the  making  of  a  varnish  consists 
in  the  following :     A  solution  of  coloring  matter  is  mixed 
with  a  solution  of  alum  and  the  aluminium-hydroxide, 
which  takes  up  the  coloring  matter,  is  precipitated  by 
soda.     This  process,  formerly  used  to  be  explained  as 
the  producing  of  a  chemical  combination,  while,  accord- 
ing to  the  modern  views,  there  is,  in  the  first  place,  a 
case  of  adsorption. 

21.  Dyeing. — Adsorption  plays  a  great  part  also  in  the 
dyeing  of  textile-fibers.     Many  dye  solutions,  when  in- 
vestigated by  L.  Michaelis  under  the  microscope,  proved 
to  be  colloids,  as,  for  example,  carmine,  naphthol-yellow, 
induline,  violet-black,  aniline  blue,  congo-blue,  bavarian- 
blue  in  a  water  solution,  scarlet  dissolved  in  alcohol,  etc. 

Fluorescin,  eosin,  toluidine  blue,  nile-blue,  methylene 
blue,  and  other  fluorescent  substances  do  not  show  any 
ultra-microscopical  particles,  but  do  show  a  light-cone. 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  45 

The  suspensions  of  chrom-yellow  and  of  ultramarin 
contain  comparatively  very  coarse  particles.  In  the  deep 
blue  "solution"  of  ultramarin,  which  appears  clear  to  the 
eye,  which  can  be  filtered  through  paper,  and  which, 
often,  does  not  settle  for  months,  small  points  can  be  seen 
even  under  an  ordinary  microscope  with  a  magnification 
of  1,200. 

L.  Michaelis  makes  the  following  interesting  conclu- 
sions from  his  ultra-microscopical  studies :  those  coloring 
matters,  which  form  colloidal  solutions  in  water,  can  be 
employed  as  elementary  coloring  matters,  and  as  such, 
which  possess  a  diffusive  power. 

Numerous  coloring  matters  cannot  readily  be  fastened 
on  the  textile-fiber,  the  material  to  be  colored  must  prev- 
iously be  subjected  to  the  process  of  mordanting.  For 
this  purpose  it  is  mostly  impregnated  with  colloidal 
aluminium  hydroxide,  which  effects  a  wash-proof  union 
between  the  coloring  matter  and  the  fiber. 

Dyeing  was  considered  from  the  point  of  view  of 
colloidal  chemistry  first  of  all  by  Otto  N.  Witt,  who  two 
decades  ago  pointed  out  the  colloidal  character  of  the 
textile-fibers.1  Later  the  theory  of  dyeing  was  devel- 
oped by  P.  S.  Zacharias  and  by  W.  Biltz. 

The  solid  fibers  behave  like  the  Gels ;  they  have  a  cell- 

1  See,  for  instance,  the  treatise  by  O.  N.  Witt,  "Zur  Theory 
des  Faerbeprocesses;"  Faerber-Zeitung,  1890-91,  No.  I. 


46  THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS 

structure  and  are  swelled  on  "steaming."  By  the  alkali 
and  acid  "fulling,"  as  well  as  by  the  previous  preparation, 
the  fibers  are  brought,  according  to  Ed.  Justin  Miller, 
into  a  jelly-like  condition,  and  by  the  mechanical  action 
of  the  fulling  they  are  cemented  and  felted  together. 
According  to  P.  S.  Zacharias,  each  direct  dyeing  takes 
place  in  two  steps:  first,  absorption,  in  which  the  color- 
ing matter  penetrates  the  swelled  up  fiber,  second,  fixa- 
tion, in  which  the  penetrated  coloring  matter  is  made 
insoluble  by  chemical  reaction  or  by  coagulation. 

The  fiber  as  W.  Biltz  states,  takes  up  comparatively 
more  substantive  coloring  matter  from  a  dilute  solution, 
than  from  a  concentrated  one.  He  showed  further  that 
in  the  case  of  dyes,  which  are  of  the  type  of  benzopur- 
purin,  the  textile-fiber  may  be  substituted  by  an  inorganic 
colloid,  as  aluminium  hydroxide,  without  causing  a  quan- 
titative change  in  the  adsorption. 

The  laws  of  adsorption  have  been  especially  investi- 
gated by  the  thorough  researches  of  H.  Freundlich.1 
He  discovered  that  the  ratio  between  the  adsorbed  quan- 
tity and  the  concentration  of  the  solution  is  expressed 
by  an  exponential  equation ;  the  constants  of  this  equation 
are  different  in  different  cases. 

1  A  grouping  of  these  investigations  is  made  by  H.  Freundlich 
in  his  book,  *  *  Kapilarchemie  "  (I/eipzig  1909). 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  47 

22.  Tanning.1 — The  animal  hide  represents  a  mixture 
of  protein-like  substances,  which  are  in  the  form  of  a 
Gel.  The  vegetable  tannins,  which  are  used  in  the  indus- 
try, are  also  in  the  condition  of  colloidal  solutions ;  con- 
sequently, tanning  represents  a  reaction,  which  takes 
place  between  colloids.  The  precipitation  processes, 
which  are  caused  in  colloidal  solutions  by  electrolytes, 
assert  themselves  even  in  the  process  of  the  extraction  of 
tannin  from  the  tannin  raw  materials  by  water;  distilled 
water  extracts  considerably  more  tannin  than  raw  water ; 
the  losses  are  the  heavier,  the  more  impurities  contained 
in  the  water,  which  is  used  in  the  process.  The  hide, 
which,  by  soaking  and  treatment  with  lime,  was  de-haired 
and  freed  from  flesh,  and  which,  by  treatment  with  acid, 
was  de-limed,  absorbs  from  the  tanning  materials,  pre- 
ferably, colloids.2  These  colloidal  tanning  materials 
(tannin,  etc.,)  are  absorbed  more  or  less  rapidly,  accord- 
ing to  their  nature,  being  taken  up,  preferably,  by  the 
upper  parts  of  the  hide,  or  penetrating  also  to  its  interior. 
Since  from  leather  which  was  tanned  by  vegetable  tan- 
nins, more  tannin  can  be  washed  out  immediately  upon 

1  A  fuller  treatment  of  the  subject  is  given  by  E.  Stiasny 
in  Koll.-Zeitsch.,  1908,  2  :  257-263. 

8  An  important  part  is  played  thereby  by  the  "swelling  up"  of 
the  fiber.  As  J.  v.  Schroeder  found  in  his  research  work,  "Zur 
Kenntniss  der  Gerbprocesse"  (Dresden,  1909),  hide-powder,  in 
order  to  be  able  to  take  up  tannins,  must  first,  be  soaked  in  water. 


48  THE:  COLLOIDS  IN  THE:  INDUSTRIAL  ARTS 

the  finishing  of  the  tanning  process,  than  after  the  leather 
has  been  stored,  it  is  to  be  assumed,  that,  in  time,  the 
adsorbed  tannin  changes  from  the  reversible-,  into  the  ir- 
reversible- Gel-form,  a  process,  which  is  catalytically 
accelerated  by  the  fibers  of  the  hide.  But  the  tannin, 
which  is  taken  up  by  the  hide,  is  surely  changed  also 
chemically;  oxydation,  anhydration,  and  polymerisation 
are  presumed  to  be  these  chemical  transformations. 
Since,  further,  diffusion  and  capillarity  are  determining 
factors  of  the  penetration  of  the  hide  by  the  tannins,  the 
process  of  tanning  appears  to  be  a  very  complicated  one, 
the  theory  of  which  is  still  obscure. 

In  mineral-tanning  chromium  salts  (chrom-tanning) 
and  alum  are  used.  The  real  tanning  material  is  the  col- 
loidally  dissolved  basic  salt.  Since  the  alum  splits  up 
less  basic  salts,  than  the  chromium  sulphate,  the  alum- 
inium salts  penetrate  the  hide  more  rapidly,  indeed,  but 
their  tanning  action  is  weaker.  While  chrom-tanned 
leather  resists  the  action  even  of  hot  water,  a  larger  por- 
tion of  the  aluminium  hydroxide  can  again  be  washed 
out  from  alum-tanned  leather;  the  longer  the  leather  is 
stored,  the  more  of  the  aluminium  hydroxide  becomes 
insoluble. 

The  fact,  that  the  iron  salts,  which  are  closely  related 
to  those  of  chromium  and  aluminium,  are  not  well  fit  for 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  49 

tanning  purposes  (the  leather  is  made  brittle),  E. 
Stiasny  traces  back  to  the  iron  hydroxide,  which  does 
not  diffuse  sufficiently  and  is  too  easily  precipitated.  By 
the  addition  of  blood  (as  a  protective  colloid)  the  iron 
tanning  can  be  improved. 

In  fat-tanning  the  colloidal  fat  (Tran,  etc.,)  is  ad- 
sorbed by  the  fiber  and  then  transformed  into  insoluble 
oxydation  products  by  the  oxygen  of  the  air.  Also  in 
this  case  we  find  the  general  principle  of  the  tanning, 
the  colloidally  dissolved  tanning  material  is  first  adsorbed, 
then  it  is  changed  into  an  insoluble  form,  so  that  the  tan- 
ning cannot  retrocede. 

The  essence  of  any  tanning  process  consists,  accord- 
ing to  the  conception  of  P.  S.  Zacharias,1  in  the  follow- 
ing: the  hide  is  transformed  into  leather  by  the  coagula- 
tion of  the  swelled  up  hide  fiber,  and  by  the  nullifying 
of  its  ability  to  take  up  water  through  an  appropriate 
deposition  of  the  tannins. 

The  processes  which  take  place  in  pickling  have 
lately  been  studied  more  closely  by  Henry  R.  Procter.2 
In  pickling,  the  hide  is  treated  with  a  very  diluted  solu- 
tion of  sulphuric  acid,  whereby  the  fibers  of  the  binding 
tissues  swell  up  strongly;  they  are  then  immersed  in  a 

1  Lecture  at  the  Fifth  International  Congress  of  Applied  Chem- 
istry, Berlin,  1903. 

2  Kolloidchemische  Beihefte,  1911,  2  :  243-284. 


5<3  THE)  COLLOIDS  IN  THE  INDUSTRIAL  ARTS 

concentrated  solution  of  salt  which  causes  contraction, 
the  fiber  is  strongly  dehydrated  and  becomes  leather-like. 
The  saturated  solution  of  salt  is  not  able  to  dehydrate  a 
hide,  which  has  not  been  subjected  to  a  preliminary 
treatment  with  acid. 

Gelatine,  which,  owing  to  its  formless  structure,  offers 
simpler  conditions  for  investigation  than  the  hide  sub- 
stance, and,  which  in  other  respects  behaves  similar  to 
the  hide  substance,  according  to  the  observations  made  by 
H.  R.  Procter,  is  able  to  take  up,  in  strongly  diluted  solu- 
tions of  muriatic  acid,  more  than  fifty  times  its  weight 
of  water,  while  in  pure  water  it  takes  up  only  seven  or 
eight  times  its  weight  of  water.  Very  dilute  acids  exert 
only  a  slight  swelling  action.  Neutral  salts  (i.  e.,  salts, 
which  have  neither  an  acid,  nor  an  alkaline  reaction), 
when  in  a  neutral  solution,  increase  the  swelling,  but, 
when  in  presence  of  a  trace  of  muriatic  acid,  they  effect, 
on  the  contrary,  a  considerable  contraction.  H.  R.  Proc- 
ter assumes,  that  gelatine,  which  acts  as  a  weak  base, 
forms  with  the  acid  a  salt-like  compound. 

23.  Soap-Manufacture. — Soap  represents  by  its  spongy 
consistency  the  typical  structure  of  a  Gel.  The  large 
quantities  of  water,  which  are  contained  in  soap,  in 
storage,  are  gradually  given  off.  But,  if,  on  the  contrary, 
dried  soap  is  placed  into  water,  it  swells  up  and  dissolves 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  51 

to  a  jelly.  This  liquefaction  process  takes  place  more 
rapidly  when,  according  to  F.  Goldschmidt,  some  alkali 
is  added  to  the  water;  this  is  the  reason  why  the  soap- 
maker  remelts  his  scrap  not  with  water,  but  with  weak 
lye. 

The  salting  out  (graining)  of  the  soap,  i.  e.,  the  sep- 
aration of  the  soap  from  the  aqueous  solution,  by  the 
addition  of  a  mixture  of  common  salt,  soda,  and  caustic 
soda,  has  hitherto  been  considered  as  an  "ion-reaction" ; 
now  this  process  is  considered  as  the  flocculation  of  a 
colloid.  That  concentrated  soap  solutions  are  of  a 
colloidal  nature,  is  proven  by  the  fact,  that  they  boil  at 
1 00°,  just  as  pure  water,  while  the  boiling-point  of  a 
true  solution  is  higher  than  that  of  the  solvent.  The 
electrical  conductivity  of  a  strong  soap  solution  is  also 
very  small  at  room  temperature,  while  otherwise  the 
alkali  salts  are  very  good  conductors.  But,  in  order  to 
avoid  misunderstandings,  I  wish  to  emphasize,  that  soap 
solutions  are  by  no  means  always  colloidal,  and  that 
there  are  various  differences. 

Owing  to  its  great  porosity,  the  soap-Gel  is  able  to 
absorb  much  water  without  appearing  moist,  which 
property  is  made  use  of  by  manufacturers.  For  adul- 
terating purposes,  various  cheap  fillers,  such  as  common 
salt,  potash,  and  sodium-silicate  may  be  added.  The 
soft  soaps,  which,  as  is  known,  are  not  solid,  but  have  a 


52  THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS 

jelly-like  consistency,  are  "filled"  with  potato-Hour, 
which  is,  indeed,  in  its  turn  perfectly  well  gelatinized  by 
the  action  of  alkalies.  The  potato-flour  is  mixed  with 
potash  and  a  solution  of  soap,  the  mixture  is  added  to 
the  soft  soap,  and  the  whole  is  crutched  till  it  is  uniform, 
when,  finally,  a  solution  of  caustic  potash  is  added.  A 
product  is  then  obtained,  which,  despite  its  high  water 
content,  has,  owing  to  the  flour-gelatine,  the  firmness  of 
a  good  article. 

24.  Brewing-Industry. — The  observation,  made  by  H. 
Bechhold,  that  colloidal  solutions  are  clarified  by  filters, 
the  pores  of  which  have  been  reduced  by  jellies,  has  been 
made  use  of  by  F.  Emslander  to  explain  certain  pro- 
cesses in  the  brewing-technic.  From  the  wort  (malt 
extract),  to  which  hops  have  been  added,  and  which  was 
boiled  with  the  hops  for  several  hours,  a  sediment  sep- 
arates upon  cooling,  the  so-called  malt-residuum  (Kuehl- 
gelaeger),  which  settles  to  the  bottom  of  the  cooling 
vessel  and  consists  mostly  of  coagulated  albumen. 
The  malt-residuum  can  be  easily  separated  from  the 
wort  by  filtering  through  coarse  linen  cloth.  On  the 
other  hand,  the  so-called  keg-residuum  (Fassgelaeger) 
which  separates  in  mellowing  of  the  beer  in  keg  storage, 
is  not  easily  separated  by  filtration,  because  its  solid  par- 
ticles are  very  small,  and  contain  very  many  bubbles  of 
carbonic  acid,  which  clog  the  pores  of  the  filter.  But 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  53 

if  the  beer  be  passed  through  a  filter,  which  already  con- 
tains the  malt-residuum,  a  perfectly  clear  filtrate  may  be 
obtained,  and  time  is  also  saved. 

Soluble  proteins  may  act  in  the  beer  as  protective  col- 
loids, and  prevent  the  flocculation  of  the  yeast;  in  such 
case  the  beer  remains  turbid. 

The  remarkable  influence  of  water  on  the  quality  and 
kind  of  the  beer  can  be  explained,  in  some  respects,  by 
colloidal  chemistry.  Water  which  contains  much  iron 
acts  harmfully  because  the  flocculated  iron  hydroxide 
carries  away  with  it  taste-  and  extractive — matters;  the 
beer  is  not  matured  (Vollmundig).  Water,  which  con- 
tains lime,  has,  on  the  contrary,  a  favorable  influence, 
because  it  improves  considerably  the  yield  from  the 
malt,  and  helps  the  maturing. 

25.  Lubricating  Greases. — If  lime  soap  (15-23  per 
cent.)  be  dissolved  in  heavy  mineral  oils,  to  which  is 
added  a  little  water  (1-4  per  cent.),  a  lubricating  grease 
is  obtained,  which  has  a  salve-like  consistency,  and  is 
used  especially  for  lubricating  inaccessible  bearings. 
Without  water,  the  solution  of  lime  soap  in  mineral  oil  is 
liquid;  under  the  ultramicroscope  it  appears  turbid.  A 
solution  of  lime  soap  in  pure  benzene  also  shows  a 
bluish  light-cone.  The  black,  non-transparent  mineral 
oils  also  appear  under  the  ultra-microscope  as  colloidal 
solutions. 


54  THE;  COLLOIDS  IN  THE:  INDUSTRIAL  ARTS 

Reddish-yellow  lubricating  oils  give  an  amicroscopic 
bluish  light-cone,  likewise  white  paraffin  oil.  Crystal- 
lized paraffin,  which  is  dissolved  in  benzene  in  smaller 
quantities,  does  not  show  a  distinct  light-cone,  but,  after 
a  considerable  quantity  of  paraffin  is  dissolved,  a  light- 
cone  appears  consisting  of  beautifully  flashing  sub-mi- 
croscopical particles. 

The  solution  of  asphalt  in  benzene  appears  dark  under 
the  ultra-microscope;  but,  if  plenty  of  alcohol  is  added 
to  it,  sub-microns  appear,  which  are,  evidently,  precipi 
tated  asphalt.     To  the  naked  eye  this  solution  appears 
clear. 

Resin  also,  when  in  an  alcoholic  solution,  exhibits  sub- 
microscopical  particles. 

If  the  water-free  solution  of  lime  soap  in  mineral  oil 
be  intimately  mixed  with  only  three-fourths  of  one  per 
cent,  of  water,  it  becomes  salve-like  in  consistency;  its 
viscosity  often  increases  with  time.  From  the  view- 
point of  colloidal  chemistry,  this  transformation  can  be 
explained  as  a  process  of  coagulation. 

In  concluding  these  observations  D.  Holde  suggests 
that  the  ultra-microscope  be  employed  in  the  examination 
of  mineral  oils,  paraffin,  ceresin,  rosins,  etc. 

Under  the  ultra-microscope,  Russian,  almost  paraffin- 


THE:  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  55 

free,  petroleum  oil,  for  example,  can  immediately  be  dis- 
tinguished from  the  American. 

26.  Sewage  Purification. — The  sewage  of  cities  con- 
tains a  large  quantity  of  organic  substances,  and,  indeed, 
the  larger  part  of  these  in  the  condition  of  colloidal  solu- 
tions. The  sewage  can  be  purified  from  these  harmful, 
putrescible  substances,  by  the  addition  of  suitable  chemi- 
cals (chemical  purification).  Since  the  putrescible 
sewage  substances  migrate  in  the  electric  current  to- 
wards the  positive  pole,  and  are  negatively  charged 
towards  water,  positively  charged  colloids  are  adapted  for 
their  precipitation,  as,  for  example,  the  hydrosol  of  iron 
hydroxide.  The  iron  hydroxide,  which  is  obtained  by 
the  decomposition  of  iron  chloride,  in  flocculation,  car- 
ries down  with  it  the  major  part  of  the  putrescible  sub- 
stances. Drinking  water  also  may  be  purified  in  the 
same  manner,  by  the  addition  of  measured  quantities  of 
iron  chloride  and  sodium  carbonate.  L.  Schweikert 
recommends,  instead  of  these  additions,  a  colloidal  solu- 
tion of  iron  hydroxide,  which  he  prepares  from  freshly 
precipitated  iron  hydroxide,  by  washing  with  water  until 
it  goes  into  solution.  With  one  litre  of  this  solution 
(which  costs  about  3  Pfennige — less  than  i  cent) 
Schweikert  was  able  to  purify  i  cm.  of  water,  taken 
from  the  river  Elbe. 

Colloidal  aluminium  hydroxide  is  also  adapted  for  use 
5 


56  THE}  COLLOIDS  IN  THE)  INDUSTRIAL  ARTS 

as  a  clarifying  agent,  for  example,  of  waste  waters  from 
starch  manufacturing  plants.1 

When  these  clarifying  agents  are  applied,  it  must  be 
taken  into  consideration  that  they,  indeed,  carry  down 
the  organic  putrescible  substances,  but  they  do  not  de- 
stroy them.  If  these  organic  substances  are  carried  away 
by  running  water  soon,  this  clarification  is  sufficient,  but, 
if  the  precipitate  remains  in  the  same  place,  putrefaction 
sets  in.  In  order  to  avoid  this,  in  such  cases,  a  purifi- 
cation agent  is  to  be  employed,  which  oxidizes  and  de- 
composes, as,  for  example,  ozone. 

In  the  chamber  process  of  sewage  purification,  the 
gradual  flocculation  of  the  organic  substances  is  made 
more  rapid  by  the  putrefaction,  which  sets  in.  The  walls 
of  the  chamber  are  covered  with  sediments  consisting 
of  rolled  together  colloids;  the  gases,  which  are  evolved 
during  the  process  of  putrefaction,  stir  up  the  sludge,  and, 
from  time  to  time,  bring  it  to  the  top,  or  hold  it  suspend- 
ed in  the  liquid.  These  sludge  particles  adsorb  on  their 
surfaces  further  quantities  of  colloids;  as  soon  as  the 
gas  escapes,  the  sludge  sinks  again  to  the  bottom.  By 
frequently  repeating  this  movement,  the  sewage  becomes 
continually  clearer. 

1  According  to  P.  Rohland,  also  the  highly  plastic  kaolins  of 
Striegan,  in  Schlesien-Germany,  thanks  to  their  richness  in  col- 
loids, can  be  used  for  clarification  of  waste  waters.  Koll.-Zeitschr. , 
1908,  2  :  177-179. 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  57 

After  this  clarification,  the  sewage  is  conducted 
through  tubes  or  through  sprinkling  filters;  these  are 
filled  with  materials  having  a  large  surface,  which  adsorb 
the  colloidal,  refuse  substances,  as  well  as  a  part  of  the 
ammonia  and  the  salts. 

If  the  purification  mass  is  coarse,  and  the  air  has  free 
access  to  the  tubes,  the  jelly-like  sediment  gradually 
becomes  granular  and  may  easily  be  rinsed  out. 

When  filters  are  employed  for  the  purpose  of  purify- 
ing water,  their  action  is  based  primarily  on  the  adsorp- 
tion-power of  the  filtering-medium,  be  it  sand,  carbon, 
wood-wool,  or  the  like;  by  depositing  themselves  on  the 
filtering  medium,  the  colloids  enlarge  still  more  the  ef- 
fective surface,  and  therewith  improve  the  adsorption. 
As  is  known,  filters  mostly  do  not  work  well  at  the  be- 
ginning, they  must,  first,  be  worked  up. 

Along  with  these  colloidal  reactions,  the  transforma- 
tions brought  about  by  bacteria,  especially  in  the  Biologi- 
cal process  of  purification  of  sewage  are,  however,  the 
most  essential  feature. 

27.  Colloids  in  Agriculture. — The  inventive  man  un- 
consciously derives  benefit  from  the  colloids,  which  are 
present  in  the  fertile  soil,  as  well  as  those  in  the  numerous 
trades.  That  very  process  of  reducing  and  etching, 
which  H.  Kuzel  employed  in  order  to  obtain  tungsten  in 
a  colloidal  condition,  is  practiced  by  nature  on  a  large 


58  THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS 

scale.  The  influence  of  the  disintegration  process,  which 
results  in  the  formation  of  colloids,  has  been  mentioned 
on  page  23.  In  addition  to  that,  there  are  other  power- 
ful forces.  The  rivers,  the  Elbe,  for  example,  in  flow- 
ing, carry  with  them  rocks  and  soil;  on  the  way  to  the 
sea,  the  soil  becomes  ever  more  finely  divided,  partly 
mechanically,  partly  by  putrefaction  processes  (in  the 
same  manner  as  in  the  process  of  mellowing  of  kaolin), 
and  at  last  the  viscous  silt  is  deposited  in  the  sea  between 
the  alluvial  land  and  the  shore;  this  deposit  is,  owing, 
probably,  to  its  extraordinary  fine  division,  an  exception- 
ally fertile  soil,  so  that  the  cost  of  building  dams  is  cov- 
ered by  the  sale  of  this  land  with  profit.  A  hectar 
(about  2 1/2  acres)  of  this  land  costs  at  present  about 
3,000  Marks  (about  $710). 

Even  usual  soil  manifests  a  large  binding  capacity  for 
the  nourishable  materials,  which  are  contained  in  irri- 
gating waters,  and,  in  general,  in  the  manures.  Accord- 
ing to  J.  M.  van  Bemmeln1,  the  ability  of  soils  to  take  up 
salts  of  the  alkalies  and  alkaline-earths  from  their  solu- 
tions is  based  on  their  content  of  basic,  soluble  in  hydro- 
chloric acid,  silicates,  which  contain  lime,  magnesia, 
potash  and  soda,  and  which  are  able  to  exchange  these 
bases  with  the  salts  contained  in  the  water.  It  is  seen, 
that  also  in  this  case,  as  in  many  others,  which  were  con- 
1  J.  M.  van  Bemmeln,  Die  Absorption  (Dresden  1910). 


THE  COLLOIDS  IN  THE  INDUSTRIAL  ARTS  59 

sidered   before,   the   chemical   transformations   enhance 
the  adsorption  action. 

The  silt  of  the  Nile  also  contains  a  considerable  quan- 
tity of  hydrated  silicates,  suitable  for  the  colloid  forma- 
tion, which  take  up  from  the  Nile-water  every  year, 
during  the  innundations,  potash,  nitrogen,  and  phosphoric 
acid  and  transfer  these  stored  up  nourishing  materials 
to  the  plants  after  the  waters  recede.  In  this  manner  Ef" 

-<¥" 

Pohl  explains  the  astonishing,  inexhaustible  fertility  oft 
the  Nile-land. 

The  great  water  absorption  ability  of  soils  rich  in  col- 
loids, which  prevents  a  too  rapid  drying  out  of  the  soil 
during  dry  periods,  and  which  in  this  way  is  useful  to 
the  plant-growth,  was  already  mentioned  on  page  40. 

It  would  be  easy  to  find  in  literature  as  well  as  in 
practice  other  cases,  in  which  the  colloids  play  an  im- 
portant part.1  However,  I  believe  that  the  birds-eye- 

1  For  example,  in  the  photographic  technics  we  find  the  re- 
markable fact  that  the  bromo-silver  gelatine  plates,  at  first,  are  not 
fit  for  use ;  they  must  be  previously  stored.  In  storing,  the  plates, 
which  are  transparent  at  the  beginning,  become  very  turbid ;  the 
ultra-microscopical  bromo-silver  particles  clump  together  into 
somewhat  larger  particles,  which  are  now  especially  light-sensitive. 
In  general,  the  colloidal  forms  of  the  silver  halogens,  their  adsorp- 
tion further  the  tanning  and  adsorption  of  the  gelatine  play  a 
weighty  part  in  the  photography.  I  only  wish,  in  a  few  words, 
to  call  attention  to  the  work  of  Luppo-Cramer,  "Kolloidchemie 
und  Photography  (Dresden  1908). 


60  THE   COLLOIDS   IN   THE   INDUSTRIAL  ARTS 

view  of  the  colloids,  which  I  have  here  presented,  is  in 
a  quantitative  way  satisfactory,  in  a  qualitative  way 
there  is  as  yet  much  to  be  desired.  In  most  of  the  cases 
we  know  very  little  of  the  real  essentials  of  the  phenom- 
ena. But  we  may  cherish  the  conviction,  that  colloidal 
chemistry,  which  is  yet  more  than  one  hundred  years 
behind  the  chemistry  of  crystalline  substances,  in  the 
future  may  be  able  to  give  the  desired  enlightment. 
Each  step  forward  in  this  dark  field  is,  directly  or  in- 
directly, of  importance  and  value  also  to  the  arts  and 
manufactures. 


INDEX 


PAGE 

Absorption  power  of  colloids,  utilization  of  the 

in  the  preparation  of  dry  batteries 39 

in   the  removal  of  disagreeable  liquids 40 

importance  of  the,  in  nature  (soil) 40 

Acheson    1 1 

Acid,  silicic,  colloidal 2,  13,  35 

silicic,   hydrosol  of 4 

stannic,  hydrosol  of 4 

tungstic,  hydrosol  of 4 

tannic    u 

Adhesi ves,  colloids  as 38 

Adhesive  power 38,  39 

Adsorption  42,  43,  44 

power  of   colloids 43 

properties  of  the  colloids  in  varnish  making 44 

properties  of  the  colloids  in  dyeing 44 

laws   of 46 

prevention    of 43 

Aggregated  dispersed  system  (See  also :  Suspension) 14 

Aggregation,  irreversible  state  of 13 

reversible  state  of 13 

Agriculture,  colloids  in 57 

Alcosol    4 

Aluminium  hydroxide,  hydrosol  of 4,  10 

Amicroscopic  particles 7 

Arsenious  sulphide,  hydrosol  of 4 

Batteries,  diaphragms  in  storage 42 

Bechhold,  H 52 

Beer,  protective  colloids  in 53 

influence  of  water  on  the  quality  of 53 

Bemmeln,  J.  M.  van 40,  58 


62  INDEX 

PAGE 

Benedicks,  C 22 

Berlin  blue,  hydrosol  ot 4 

Biltz,   W 45,  46 

Blake,  J.  C 17 

Bredig,   G 7,  17 

Brewing  industry,  colloids  in  the 52 

Casting  glass-melting  pots,  Weber's  process  of 33 

Cell-structure    2 

Cell  walls,  plant,  as  colloidal  diaphragms 41 

Cement,  colloidal 36 

hardening  of,  in  sea-water 38 

Michaelis'  theory  of  the  hardening  process  of  hydraulic  35 

Stern's  theory  of  the  setting  of 35 

Ceramic  industry,  colloids  in  the 32 

Clarifying  agents  in  the  purification  of  water  and  sewage....  56 

Clay,   liquefaction   of 34 

Coloration,    glaze 22 

interpretation  of  the  process  of,  in  gold  ruby  glass 19 

in  copper  ruby  glass 21 

Colors,  protective  colloids  in  the  manufacture  of  water n 

Colloid,  definition  of  the  term I 

Colloids,   emulsion 16 

protective    16 

protective,  in  beer 53 

protective,  in  fine  mechanical  suspensions n 

suspension  16 

as   adhesives    38 

as  diaphragms  38 

as  filters   41 

as  glues  38 

adsorption  power  of 43 

adsorption,  utilization  of,  in  the  preparation  of  dry  bat- 
teries    39 


INDEX  63 


Colloids  —  (continued) 

adsorption,  utilization  of,  in  the  removal  of  disagreeable 

liquids    ..........................................  40 

surface   development   of  ..............................  17 

in  agriculture  .........................................  57 

in  the  absorption  of  liquids  ...........................  39 

in   the  ceramic  industry  ..............................  32 

in   mineral  kingdom  ..................................  23 

in  photographic  technic  ...............................  57 

peptisation   of  ........................................  33 

Colloidal  cement    ..........................................  36 

Colloidal  character  of  textile  fibers  ..........................  45 

diaphragms,  plant  cell  walls  as  ........................  41 

silicic  acid    ..........................................  2 

solutions   .......................................  2,  3,  7 

solutions,  clarification  of  .............................  52 

solutions,  flocculation  of  ..............................  8 

solutions  of  metals  ...................................  4 

solutions  of  platinum  .................................  8 

solutions  of  silver,  preparation  of,  by  method  of  Lea...  12 

solution  of  sodium  ...................................  8 

Concentration  limit,  of  emulsoids  ...........................  17 

of   suspensoids    ......................................  16 

Condenser,  kardioid    .......................................  5 

paraboloid    ...........................................  5 

Copper  ruby  glass  ..........................................  21 

interpretation  of  the  coloration  process  in  ............  21 

Cornu,  F  ................................................  23,  24 

Cowper-Coles,  S  ...........................................  26 

Crystalline    antitypes    ......................................  24 

forms    ...............................................  i 

state    ................................................  i 

Curdling  of  milk  ...........................................  12 

Curing,  see:  Mellowing  of  porcelain  clay. 

Dehydration  of  peat  by  electro-osmosis  ...................  40,  41 


64  INDEX 

PAGE 

Dialysis  3,  12,  42 

Diaphragms,  artificial  , 41,42 

in  nature.     See:  Plant  cell  walls. 

in  storage  batteries 42 

Diffusion  41 

power  of  colloidal  solutions 15 

Dispersing  medium  14 

phase  14,  16 

Dispersed  systems  14 

Doelter,  C 23 

Ductility  of  pure  tungsten  32 

Dyeing  44,  45 

theory  of,  by  Zacharias  and  Biltz 45 

Electro-osmosis,  dehydration  of  peat  by 40,  41 

Emslander,  F 52 

Emulsion-colloids    16 

Emulsions,  viscosity  of   16 

Emulsoids    16 

Energy,  surface   17 

Faraday,   M 4 

Fibers,  colloidal  character  of  textile 45 

Filaments    26 

Kuzel's  process  for  the  manufacture  of  metallic 29 

Filters 42 

gels  as 41,  57 

Flocculation  process,  importance  of  the,  in  physiological  chem- 
istry   . .  _ ii 

Flocculation,  of  an  amicroscopic  solution  of  gold 7 

of  colloidal  solutions 8,  9,  51 

of  hydrosols  of  metals 25 

of   suspension-colloids    16 

Foams    17 

Freundlich,  H 46 

Fulling    46 


INDEX  65 

PAGE 

Gel    ^ 4,   12,  14,  23,  24,  26,  29,  32 

Gels,  as  diaphragms  41 

as  filters   41 

distribution  of,  in  mineral  kingdom 24 

mineral.    See  also :   colloidal  cement 24 

soap    51 

solid    fibers    as 45 

Germs,  formation  of  gold 19,  20 

in  spoiled  ruby  glass  21 

Glass-melting    pots,    Weber's    process    for    the    manufacture 

of,  by  casting  33 

Glass,  milky-white  opaque  21 

quartz   I,  35 

ruby    18 

Glassy  state   I,  2 

Glaze-colorations    22 

Glue    i,  2 

fish    13 

Glueing 38 

Glues,  colloids   as 38 

Gold,  colloidal  solution  of   4,  5 

flocculation  of  an  amicroscopic  solution  of 7 

preparation  of  colloidal  solutions  of,  by  the  method  of 

R.  Zsigmondy  4 

ruby  glass    18 

ruby  glass,  interpretation  of  the  coloration  process  in..  19 
ruby  glass,  discernment  of  the  ultra-microscopical  gold- 
particles  in,  by  Siedentopf  and  Zsidmondy 18 

ruby  glass,  preparation  of  genuine  18 

Goldschmidt,  F 51 

Graham,  Th I 

Graining  of  soap  51 

Graphite,  protective  colloids  in  the  preparation  of,  as  a  lubri- 
cating material 1 1 


66  INDEX 


PAGE 
Greases,   lubricating    53 

Hardening,    Michaelis'   theory   of   the,   process   of    hydraulic 

cements    35 

of  cement  in  sea-water 38 

Hide,  animal   47 

fiber,  swelling  up  of  47 

Holde,  D 54 

Honey-comb  structure  2,  12 

Hydrosol,  of  aluminium  hydroxide 4 

of  Berlin  blue  4 

of  gold    ii 

of  iron  hydroxide  4 

of  iron  in  the  purification  of  water  and  sewage 55 

of  metals,  Bredig's  method  of  preparation  of  7 

of  metals,  flocculation  of,  in  the  preparation  of  gold 

and  silver  mirrors  25 

of  silver 8 

of  stannic  acid 4 

of  tungstic  acid   » 4 

Ions,  precipitating  power  of 10 

Iron  carbide    22 

Iron  salts  in  tanning 48,  49 

Iron  tanning 49 

Jelly    i,    2 

inorganic    2 

organic    2 

Kaolin,  Putrefaction  process  in 32 

Kardioid-condenser   5 

Ultramicroscope    22 

Keg  residuum  52 


INDEX  67 

PAGE 

Keppeler,  J 34 

Kuzel,  H 29,  57 

Lamps,  incandescent  27 

metallic  filament    27 

osmium    28 

osra 31 

tantalum    27 

tungsten 26 

tungsten,  manufacture  of 26 

siriuscolloid    31 

Lea,  C " 12 

Leather,   chrom-tanned    48 

Lighting  industry,  aspiration  of 27 

Liquefaction  of  clay  34 

of  soap   51 

Liquid  state   2 

Lottermoser,  A 21,  31,  32 

Lubricating  greases  53 

Luppo-Cramer ^ 59 

Magnitude  of  ultra-microscopical  gold-particles. 6 

Malt-residuum  52 

Martensite   22 

Medium,  dispersing  14 

Mellowing  of  porcelain  clay 33 

Membrane,   parchment   3 

Mercury,  colloidal   1 1 

Metal  alloys  22 

Metals,  colloidal  solutions  of,  in  the  preparation  of  gold  and 

silver  mirrors   25 

preparation  of  hydrosols  of,  by  the  method  of  Bredig. .     7 

Michaelis,  L 44,  45 

Michaelis,  W 35,  36 


68  INDEX 


PAGE 

Micron  6 

Microscope,  ultra- 5,    6 

Migration-sense    10 

Milk,  curdling  of  12 

Miller,  E.  J 46 

Mirror,  gold 25 

hollow  metallic  26 

hollow  metallic,  manufacture  of,  by  the  method  of  Cow- 
per-Coles  26 

silver    25 

Molecule  of  chloroform 6 

of  soluble  starch 7 

Molecular  dispersed  system.    See  also :    True  solutions 14 


Nicol-prism    15 

Nile,  silt  of  the 59 

Opal    23 

Organic  jellies ^ 2 

Ore-bed   24 

Osmium  lamps,  preparation  of  filaments  for 28 

Osmond,  F 22 

Oxy-hydrogen  flame  I 

Paraboloid  condenser  5 

Parchment  membrane 3 

Particles,  amicroscopic  7 

starch   6 

ultra-microscopic  6,  16 

Pearlite    22 

Peat,  dehydration  of,  by  electro-osmosis 40,  41 

molds    40 

pressing  of  40 


INDEX  69 

PAGE 
Peptisation  of  colloids 13,  33 

Weber's  application  of  the,  in  the  manufacture  of  glass- 
melting  pots  by  casting 33 

Percolation  42 

Permeability 42 

Pharmaceutical  industry,  protective  colloids  in  the u 

Phase,  dispersed   14,  16 

Phosphorus,  yellow  4 

change  of  white,  into  red 22 

Protographic  technic,  colloids  in  the 59 

Physiological  chemistry,  importance  of  flocculation  process  in.   n 

Pickling  49 

Plant  cell  walls  as  colloidal  diaphragms 41 

Platinum,  colloidal  solution  of 8 

Pohl,   E 59 

Porcelain    clay    32 

storing   of    32 

Potato-flour  as  a  soap  filler 52 

Power,  adhesive 38,  39 

diffusion,  of  colloidal  solutions  15 

Procter,  H.  R 49,  50 

Protective-colloids    1 1 

in  mechanical  suspensions  n 

Protein,  coagulation  of   12 

solution  of   II 

Psilomelane    24 

Purification  of  water  and  sewage 56 

Putrefaction  processes  , 58 

in  kaolin 32 

Quartz-glass I,  35 

Receipt  for  making  a  varnish 44 

Rock-crystal  I 


7O  INDEX 

PAGE 

Rock-salt,  Siedentopf's  explanation  of  the  coloration  of 21 

Rohland,  P 33,  35,  38,  56 

ruby-glass 18 

gold    18 

preparation  of  genuine 18 

copper 21 

Salt,  Siedentopf's  explanation  of  the  coloration  of  rock  21 

Salting,  see :  graining  of  soap 

Sapphires    23 

Schweikert,   L 55 

Schwerin,  Prince  Botho 41 

Setting  of  cement,  Stern's  theory  of   37 

Sewage-purification   55 

biological    57 

chamber  process  of 56 

chemical    55 

Shrinking  of  colloids  in  the  drying  kiln 35 

Siedentopf,  H 5,  6,  18,  21,  22 

Silicic  acid,  colloidal  2 

Silt  of  the  Nile 59 

Silver,  hydrosol  of  8,  1 1 

preparation  of  colloidal,  by  the  method  of  C.  Lea 12 

Slime    14 

Soap,  gel  51 

fillers    51 

manufacture,  colloids  in  the 50 

Sodium,  blue  colloidal  solution  of 8 

silicate    I,     3 

Soil,  binding  capacity  of,  for  nourishable  materials 58 

colloids  in  the  24 

importance  of  the  water  absorption  ability  of  colloids 

in    40,  59 


INDEX  71 

PAGE 

Sol     4 

irreversible  13 

keeping  qualities  of  metallic 8 

reversible    13 

Soldering    38 

Solution    4 

colloidal    2,    3 

colloidal,  of  metals  4 

colloidal,  of  gold  8 

Solvent    14 

Soot,  suspension  of,  in  water 1 1 

Spar,  fluor   21 

Spraying,  electrical   17 

Sprinkling  filters   57 

Stannic  acid,  hydrosol  of   4 

Starch-particles     6 

State,  amorphous 2 

colloidal    I,    2 

crystalline     T 

glassy   I 

liquid    2 

solid  non-crystalline   2 

of  aggregation,  irreversible  13 

of  aggregation,  reversible  13 

of  rest  of  silicic  acid 2 

Stern,   E 36 

Stiasny,   E 47,  49 

Stones,  precious  23 

Structure,  cell  2 

honey-comb     2,  12 

Sub-microscopical   particles    6 

Sugar,  beet,  manufacture  41 

Surface  development  of  colloids 17 

Surface  energy  17 

6 


72  INDEX 

PAGE 

Suspension    14 

colloids    16 

colloids,  flocculation  of   16 

mechanical    1 1 

porcelain  clay   6 

Suspensoids 16 

concentration  limit  of 16 

System,  aggregated  dispersed.     See  also :  Suspensions  14 

dispersed   14 

molecular  dispersed.     See  also :  True  solutions 14 

Swedberg,   Th 8 

Swelling  value    9 

Tannic  acid   1 1 

Tanning    47 

essence  of  any,  process 49 

fat   49 

iron     49 

iron  salts  in  49 

mineral    48 

Tannins,  extraction  of  47 

vegetable   47 

Tantalum    27 

lamps    27 

lamp,  preparation  of  filaments  for 28 

Textile-fibers  2 

fibers,  colloidal  character  of  45 

Topaz,  smoky,  yellow  23 

Toxins    ii 

Tridymit    35 

Troostite  22 

True  solutions 3,  14,  T5 

Tungsten    27,  32 

ductility  of  pure 32 

oxy-chloride    28 


INDEX  73 

PAGE 

Tungstic  acid,  hydrosol  of  4 

Tyndal  effect  15 

Ultra-microscope  5,    6 

in  the  examination  of  mineral  oils,  etc 54 

Ultra-microscopic  particles   6,  16 

of  gold,  Siedentopf  and  Zsigmondy's  experiment  to  dis- 
cern, in  gold  ruby  glass 18 

Varnish,  receipt  for  making  of  a 44 

making,  adsorption  properties  of  the  colloids  in 44 

Viscosity  of  emulsions  16 

Visibility,  limit  of,  of  metallic  particles  7 

Waterglass,  (See  Sodium  silicate.) 

Weber,  E 33 

Whitney,  W.  R 17 

Witt,  O.  N 45 

Zacharias,  P.  S .45,  46,  49 

Zsigmondy,  R 4,  6,  7  16,  18 


SCIENTIFIC  BOOKS 

PUBLISHED  BY 

THE   CHEMICAL   PUBLISHING   CO. 
EASTON,  PA. 


ARNOLD— The   Motor  and  the  Dynamo.    8vo.     Pages  VI  +  178.     166  Fig- 
ures       $1.50 

BENEDICT— Elementary  Organic  Analysis.    Small  8vo.    Pages  VI  +  82. 

15  Illustrations $1.00 

BERGEY— Handbook  of  Practical  Hygiene.    Small  8vo.    Pages  164  ....  $1.50 

BILTZ  — The    Practical   Methods   of    Determining   Molecular   Weights. 

(Translated  by  Jones).  Small  8vo.  Pages  VIII  +  245.  44  Illustrations  .  $2.00 

BOLTON— History  of  the  Thermometer.  i2mo.    Pages  96.   6  Illustrations  .  $1.00 

CAMERON— The  Soil  Solution,  or  the  Nutrient  Medium  for  Plant  Growth. 
8vo.    Pages  VI+is6.    3  Illustrations $1.25 

COLBY — Reinforced  Concrete  in  Europe.    8vo.     Pages  X  +  260 $3-5° 

EMERY— Elementary  Chemistry.  i2mo.  Pages  XIV  +  666. 191  Illustrations  .  $1.50 

ENGELHARDT— The  Electrolysis  of  Water.    8vo.    Pages  X  +  140.    90  Il- 
lustrations     $1.25 

FRAPS— Principles  of  Agricultural  Chemistry.    8vo.    Pages  VI  +  493.     94 

Illustrations $4.00 

OILMAN— A  laboratory  Outline  for  Determinations  in  Quantitative  Chem- 
ical Analysis.    Pages  88 $0.90 

GRAVES— Mechanical  Drawing.    8vo.     Pages  VI  +  139.    98  Figures  and 

Plates $2.00 

GRAVES— Orthographic  Projection.    8vo.    Pages  89.    75  Figures $1.50 

GUILD— The  Mineralogy  of  Arizona.  Small  i2tno.  Pages  104.  Illustrated  .  $1.00 

HALLIGAN— Elementary  Treatise  on  Stock  Feeds  and  Feeding.  8vo.    Pages 
VI  +302.    24  Illustrations $2.50 


HALLIGAN— Fertility  and  Fertilizer  Hints.  8vo.     Pages  VII  +  155.     12  Il- 
lustrations      $1-25 

HALLIGAN— Soil  Fertility  and  Fertilizers.      8vo.      Pages  X  +  398,      23 

Figures $3.5° 

HARDY — Infinitesimals  and  Limits.     Small  i2mo.     Paper.    Pages  22.    6 

Figures $0.20 

HART — Chemistry    for  Beginners.     Fifth  Edition.    Small   i2mo.     Vol.  I. 

Inorganic.     Pages  VIII  4-  214.    55  Illustrations.     2  Plates $1.00 

HART— Chemistry  for  Beginners.     Small  i2mo.     Vol.  II.     Pages  IV  +  98. 

ii  Illustrations $0.50 

HART— Second  Year  Chemistry.    Small  I2mo.    Pages  165.  31  Illustrations  .  $1.25 
HART,  R.  N.— Welding.     8vo.      Pages  XVI  +  182.    93  Illustrations  .   .   .   .$2.50 

HEESS— Practical  Methods  for  the  Iron  and  Steel  Works  Chemist.    Pages 

60 $1.00 

HILL— A  Brief  Laboratory  Guide  for  Qualitative  Analysis.     Small  121110. 

Pages  VI  +  80 $1.00 

HINDS— Qualitative  Chemical  Analysis.    8vo.     Pages  VIII  +  266 $2.00 

HOWE— Inorganic  Chemistry  for  Schools  and  Colleges.  8vo.  Pages  VIII  + 


$3.00 


JONES— The  Freezing-Point,    Boiling-Point  and    Conductivity   Methods. 

Pages  VIII  +  76.     2d  Edition,  completely  revised $1.00 

KRAYER— The  Use  and  Care  of  a  Balance.     Small  I2mo.     Pages  IV +42. 
18  Illustrations $°-75 

LANDOLT— The  Optical  Rotating  Power  of  Organic  Substances  and  Its 

Practical  Applications.    8vo.     Pages  XXI  -f  751.    83   Illustrations  .   .  $7.50 

LEAVENWORTH— Inorganic  Qualitative  Chemical  Analysis.    8vo.     Pages 

VI  +  153  -    •  • $1.50 

LE  BLANC— The  Production  of  Chromium  and  Its  Compounds  by  the  Aid 

of  the  Electric  Current.    8vo.    Pages  122 $1.25 

MASON— Notes  on  Qualitative  Analysis.    Small  I2mo.     Pages  56 $0.80 

MEADE — Chemist's  Pocket  Manual.     I2mo.    Second  Edition.     Pages  XII 

+  444.    39  Illustrations $3.00 

MEADE— Portland    Cement.     Second    Edition.     8vo.    Pages    X   +    512. 

169  Illustrations $4.50 


MOISSAN— The  Electric  Furnace.  Svo.  Pages  10  +  305.  41  Illustrations  .  .  $2.50 

NIKAIDO— Beet-Sugar  Making  and  Its  Chemical  Control.    Svo.     Pages  XII 

+  354-    65  Illustrations $3.00 

NISSENSON—  The  Arrangement  of  Electrolytic  laboratories.    Svo.    Pages 

Si.    52  Illustrations $1.25 

NOTES— Organic  Chemistry  for  the  laboratory.    Svo.     Pages  XII  -f  292. 

41  Illustrations $2.00 

NOTES    AND    MULLIKEN— Laboratory   Experiments  on  Class  Reactions 

and  Identification  of  Organic  Substances.    Svo.    Pages  81 $0.50 

PARSONS— The  Chemistry  and  Literature  of  Beryllium.    Svo.    Pages  VI 

-f  180 $2.00 

PFANHAUSER— Production    of   Metallic    Objects    Electrolytically.      Svo. 

Pages  162.    100  Illustrations $1.25 

PHILLIPS— Chemical  German.    Svo.    Pages  XI  -f  241 $2.00 

PHILLIPS— Methods  for  the  Analysis  of  Ores,  Pig  Iron  and  Steel.    Second 

Edition.    Svo.    Pages  VIII  -f  170.    3  Illustrations $1.00 

PRANKE — Cyanamid,  (Manufacture,  Chemistry  and  Uses).    Svo.    Pages 

VI  -f- 112.    8  Figures     $1.25 

SEGER— Collected  Writings  of  Herman  August  Seger.    Papers  on  Manu- 
facture of  Pottery.    2  Vols.    Large  Svo $7.50  a  vol.  or  $15.00  a  set 

STILLMAN— Engineering  Chemistry.    Fourth  Edition.    8vo.    Pages  X  + 

744.    175  Illustrations $5.00 

TOWER— The  Conductivity  of  Liquids.    Svo.    Pages82.    20  Illustrations  .  .$1.50 

VENABLE— The  Development  of  the  Periodic  Law.    Small  i2mo.     Pages 

VIII  +  321.    Illustrated $2.50 

VENABLE— The  Study  of  the  Atom.     I2mo.     Pages  VI  +  290 $2.00 

VTJLTE  AND  GOODELL— Household  Chemistry.    Second  Edition.    i2mo. 

Pages  VI  +  190 $1.25 

WILEY — Principles  and  Practice  of  Agricultural  Chemical  Analysis.    Vol. 

I.    Soils.    Pages  XII  +  636.    55  Illustrations.    17  Plates $4.00 


WILEY— Principles  and  Practice  of  Agricultural  Chemical  Analysis.  Vol. 
II.  Fertilizers  and  Insecticides.  Pages  684.  40  Illustrations.  7 
Plates $4.50 

WILEY— Principles    and   Practice  of  Agricultural  Analysis.      Vol.    III. 

Agricultural  Products.    Pages  XVI  +  846.     127  Illustrations $6.00 

WYSOR— Analysis  of  Metallurgical  and  Engineering  Materials, — a  Sys- 
tematic Arrangement  of  Laboratory  Methods.  Pages  82.  Illus- 
trated   $2.00 

WYSOR— Metallurgy,  a  Condensed  Treatise  for  the  Use  of  College  Students 
and  Any  Desiring  a  General  Knowledge  of  the  Subject.  Pages  308. 
88  Illustrations $3.00 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


AN  INITIAL  FINE  OF  25  CENTS 

WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
THIS  BOOK  ON  THE  DATE  DUE.  THE  PENALTY 
WILL  INCREASE  TO  SO  CENTS  ON  THE  FOURTH 
DAY  AND  TO  $I.OO  ON  THE  SEVENTH  DAY 
OVERDUE. 


OCT 


DEC  181936 


AUG    5  1938 


YC   18723 


ITY  OF  CALIFORNIA  IvIBRAR\ 


